Trailer Wiring Diagrams

Trailer Wiring Connectors

Various connectors are available from four to seven pins that allow for the transfer of power for the lighting as well as auxiliary functions such as an electric trailer brake controller, backup lights, or a 12V power supply for a winch or interior trailer lights. Choose a connector that has the required number of pins for the functions required for your trailer. If the connector is under the vehicle, you will want to use a mounting bracket to attach it to the vehicle. This will help prevent damage that may occur if the connector is left dangling.

This chart is a typical guide, wire colors may vary based on manufacturers. Use a circuit tester to verify connections.

*NOTE: The fifth connection is sometimes used on 5-ways to power a reverse lockout on trailers with surge brakes. When this is the case, the lockout should be connected to the backup light circuit of the tow vehicle.

4-Way Connectors

4-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake lights) plus one pin is provided for a ground wire. Most standard light duty trailers will use a 4-pole flat connector.

4-Way Flat Trailer Connector

4-Way Flat Trailer Connector

4-Way Round Trailer Connector

4-Way Round Vehicle Connector

5-Way Connectors

5-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake) and, besides the ground, one pin is available to provide support for another function. Typically the 5-Way Flat is used for trailers with surge brakes or hydraulic brakes. The additional wire is tapped into the backup lights to disengage the hydraulic trailer coupler (actuator) when the vehicle is reversing, thus turning off the trailer's brakes.

5-Way Flat Trailer Connector

5-Way Flat Vehicle Connector

5-Way Round Trailer Connector

5-Way Round Vehicle Connector

6-Way Connectors

6-Way connectors are available allowing the basic hookup of the three lighting functions (running, turn, and brake). The ground and two extra pins are available to provide two additional functions, typically for electric brakes and 12 volt "hot" lead. The 6-way round connectors are very common on horse trailers. The 6-way square connectors are more common on campers.

6-Way Trailer End

6-Way Vehicle End

6-Way Square Trailer and Vehicle Ends

Note: In some applications, the black battery power connection and the blue brake controller output connection are reversed.

7-Way Connectors

Aside from the three main lighting functions, additional pins for electric brakes, a 12 volt "hot" lead, and backup lights are available. There are two types of 7-way connectors. One has flat pins, which are often referred to as blades. The other has round pins. The round pin style is very rare. The RV style 7-way with flat pins (or blades) is very common. It is often found on newer trucks and SUVs that come equipped from the factory with a trailer hitch.

7-Way Round Trailer Connector (Flat Pin)

7-Way Round Vehicle Connector (Flat Pin)

7-Way Round Vehicle Connector (Round Pin)

Note: To ensure that your trailer connector is wired properly, we recommend using a circuit tester to match pins by function. Because wire colors can vary, they are not as reliable for determining functions. And improperly connected wiring can cause damage to electric components.

Mounting Your Trailer Wiring Harness

Often the 4-pole trailer connector will remain in the trunk or cargo area of a car or SUV when not in use. This helps to extend the life of the connector by protecting it from the elements and accidental damage. When it is needed for towing, simply pull the connector out and shut the trunk or rear door. The rubber weather strip that provides a door seal keeps the wire from getting pinched. If the trailer connector needs to be mounted under the vehicle, we offer many different mounting brackets that will help to protect the connector and keep it from dangling beneath the vehicle.

Trailer Wiring Adapters

The T-One connectors and hardwire kits all use a 4-pole trailer connector. This connector is most common among the smaller utility trailers and can easily be adapted to match the larger 5-pole, 6-pole and 7-pole styles. Using an adapter lets you avoid having to splice into the vehicle's wiring system. Adapters will plug into the flat 4-pole connector and have wire leads to provide additional functions such as powering trailer brakes, power lead for utility lights, reverse, or auxiliary power for a winch or tools. If your vehicle or trailer is equipped with something other than a 4-way plug, such as the larger 7-way round plug, you can use our adapter fitguide to find the one that is right for your vehicle and trailer.

Troubleshoot Your Trailer Wiring

Watch now: Troubleshoot modulite wiring

If you have a Modulite (powered converter), Converter, or T-One connector that is not working properly, you need to use a circuit tester to determine the source of the problem.

Check to make sure there is a signal going into and coming out of the converter or Modulite box without the trailer hooked up. The only part of the wiring harness that will typically go bad is the box, so you need to determine if a signal is making it to the box, and if so, is it coming back out on the correct wires. There are four possibilities:

Problem: There is no signal going into the box, meaning something is incorrect on the vehicle.Solution: Solve the problem by checking for blown fuses and then check the installation points. Use a circuit tester to check that the correct wires are tapped into, the wiring harness connectors are plugged into the correct vehicle connectors, and check that connectors are plugged in all the way.
Problem: If a signal is going in and coming out on the appropriate wires, then there is a problem with the trailer wiring. Solution: Solve the problem by inspecting the wiring on the trailer to make sure all of the connections are correct and ground wires are connected properly. Most likely, the ground wire on the trailer is not secured properly. A trailer wiring system is grounded to the frame near the coupler and each light also needs to be grounded. If there is not a white ground wire coming out of a trailer light, then the light is grounded through its mounting studs. Too much paint, dirt, or rust can cause bad grounds, so make sure the ground is secured to the bare metal frame. Also look for pinched or cut wires; these are often found when wires are routed above suspension components or behind taillights.
Problem: If a signal is going into the box and not coming out or a signal is going into the box and coming out on the wrong wires the ground on the vehicle may not be connected properly. If the white ground wire is not installed properly on the vehicle, then the green and yellow wires will not carry signal coming out of the box. Solution: Solve the problem by checking to make sure the ground wire is installed properly on the vehicle. To make sure you have a suitable ground, first connect the circuit tester's ground wire to the same location as the ground wire on the wiring harness. Then test the signal going into the converter or modulite box. If there is no signal, connect the circuit tester to another grounding location such as the exhaust pipe. If a signal is present, the grounding location for the wiring harness is bad, and a new location needs to be found. On a few vehicles, the frame and body components are not grounded. In these rare instances, look for a ground wire coming out of the license plate light.

*Due to extensive testing and quality control, it is very rare that a new wiring harness will be defective. If the wiring harness worked properly when installed but then went bad, there is a strong possibility that it has shorted out because of a problem with the trailer wiring. Make sure to correct any trailer wiring problems before installing a new wiring harness.

Issue: Converter Shorting Out

When too many amps are drawn through the converter box, it can be shorted out. The possible causes are:

Too many lights on the trailer. Each incandescent taillight draws about 2 amps and side marker lights typically draw about 0.5 amps each. Most converters allow up to 4 amps to pass through them. A standard converter cannot have any more than 1 taillight on each side.
Water. Trailer connectors get wet, causing too many amps to be pulled through the converter. Water can unite all 4 wires on the trailer connector causing it to draw too many amps. This often happens when a boat trailer is backed into water with the trailer wiring still connected to the vehicle. To solve the problem of connections getting wet, always disconnect the trailer connections before backing into the water. Also, covers can help prevent water from getting into trailer connectors when it rains or when a vehicle is taken through the car wash.
Bare wires touch each other or the trailer frame. This causes too many amps to be pulled through the converter box. The coating on trailer wires can wear thin, often at the connection to the trailer's taillight or where the wires pass over the trailer suspension. If wires are hung too loosely, they can get pinched and smashed between the trailer frame and suspension U-bolts. To solve the problem, inspect the trailer wires and replace any that are damaged or frayed.

Issue: Weak Ground

Watch now: How to Wire the Ground

If you find some, but not all, lighting functions work properly you may have a ground problem. In this situation a weak ground is just strong enough to provide some lighting functions but not all. When the taillights and brake lights are used at the same time, it creates the maximum amp load of the lights on the trailer. If a ground problem exists, it will show at this point. The places to check grounds are as follows:

The connector on the vehicle should have a ground wire secured tightly to a clean surface on the frame. A wire attached to the body or a surface with undercoating or rust can cause a ground problem.
The connector on the trailer should have a wire from the connector secured tightly to a clean surface on the trailer.
Each tail lamp assembly at the back of the trailer also must be grounded. This is done in one of two ways. The first is by a separate wire coming from the back of each tail lamp assembly being secured to the frame. The second, and most popular, ground is achieved through the bolts of the tail lamp assembly. In this case, the lamp housing must be attached to the frame of the trailer. If the lights are mounted on wood or PVC material, the light will not receive ground.
The last possibility to explore is in the trailer design. If the trailer has a tilting bed, it is possible the ground is not passing through the pivot point, resulting in a poor ground. The solution to this is to route a ground wire from the connector at the front of the trailer to each lamp assembly at the back of the trailer, bypassing this pivot point.

NOTE: If you purchased your wiring harness from etrailer.com and none of these fix your problem please feel free to contact us so our product experts, and installers can determine possible remedies or warranty coverage.

How to Wire your Car or Truck to Pull a Trailer

By law trailers are required to have at least running lights, turn signals, and brake lights. To provide the power and a connection for these functions, the tow vehicle's electrical system needs to be tapped into. There are two options available for connecting to your vehicle's electrical system, a plug-in style T-One connector or a custom hardwire kit.

T-One Connector

The easiest way to make this connection is with the use of a T-One Connector, which comes with OEM style connections that simply plug into your vehicle's existing wiring harness, typically near the rear of the vehicle or by the tail lights. Sometimes the vehicle manufacturer will run the wires to an easily accessible plug underneath the vehicle or behind the paneling in the back cargo area. T-Ones come pre-wired with a 4-way flat trailer connection and can be expanded to 5-way, 6-way, or 7-way trailer connections through the use of a wiring adapter.

Custom Hardwire Kit

If a T-One is not available, a connection can still be easily made by using one of our custom selected hardwiring kits. We offer kits with all the pieces you will need to simply tap into the existing wires on your vehicle. This may sound difficult, but quick splices make installing the wiring harness quick and easy. A quick splice has two grooves in it; one groove is for the vehicle wire, and the other groove is for the wire on hardwire kit. Once both wires are in the grooves, you simply press down on the top of the quick splice. This forces a metal piece into both wires, connecting the circuit and eliminating any need for cutting or splicing.

To hardwire the tow vehicle for a trailer connector you need to locate the proper wires. To help in this task you can check the vehicle's owner manual or use a circuit tester. The circuit tester is used to make sure the correct wires on the hardwire kit are connected to the matching wires on the vehicle; it helps determine which wire performs which function. The easiest place to tap into the vehicle's wiring system is behind the tail lights. By turning on the left turn signal, a circuit tester can be used to test the different wires behind the driver's side tail light. When the circuit tester lights up, you know that wire carries the left turn function. A quick splice slid through the yellow wire on the trailer connector and around the just found vehicle wire will clamp down to provide a secure connection.

The three types of hardwire kits are:

Standard 4-Pole Wiring Harness - For use with vehicles that have adequate power and standard wiring system, these simply connect into existing wires on the vehicle and have a 4-pole flat connector to attach a trailer.
Converter - For use with vehicles that have separate turn and brake light wires. Some vehicles send only one signal per wire, creating what is called a 3-wire system: one wire for the left turn, one wire for the right turn, and one wire for the brake signal (common on vehicles with amber turn signals). A converter will reduce it to a standard 2-wire system needed for wiring a trailer. There are still additional wires for the running lights and for the ground. Any vehicle with amber turn signals will need a converter. However, there are some vehicles with all-red tail lights that can also require a converter. A wiring harness with a converter has a black box built in it. Five wires go into the box, and only 4 come out. The converter transfers the brake signal on the vehicle into the left and right turn signals for the trailer wiring system.
Modulite or Powered Converter - Used with vehicles that do not provide enough electrical power to handle the additional strain of powering trailer lights, the Modulite or powered system draws power directly from the battery but still connects to the vehicle's wiring system to determine when to power the lights on the trailer. If there are too many lights on the trailer for the vehicle's electrical system to provide adequate power, use a modulite or powered converter. A modulite installs the same way as a standard converter except an extra wire must be run to the battery. Instead of drawing power from the vehicle wiring system, a modulite draws power directly from the vehicle battery. This is safer because the extra amps to power the trailer are no longer going through the expensive electrical components of the vehicle. More vehicles are using thinner gauge wire and require a modulite, regardless of how many lights are on the trailer, simply to protect their wiring system.

Vehicle manufacturers have intermittently changed wiring colors over the years. We recommend you use a circuit tester on the tow vehicle's wiring harness to verify that the correct wire has been located for the proper function.

Skyler R.

12/5/2022

I'm having trouble wiring in a new 7 pin plug on my pressure washer trailer. I only have 6 wires: Red White Black Yellow Green and Brown. When I hook the connector to my truck, one tail light comes on, no brake lights and turn blinkers on they all blink. Guess I need to know what the color codes are and if it could be a ground somewhere else. Thanks

Mike L.

12/5/2022

Use a circuit tester like # 40376 on the connector on the vehicle as a helper activates each taillight function. The pinout is shown in the help article I've linked for you. The fact that everything blinks with the turn signals is most likely caused by a poor ground connection. You'll want to check the main ground on the trailer tongue as well as the ground for each lamp to make sure they're securely made to clean metal. If the help article doesn't illuminate things for you (sorry for the pun), let me know and we'll look into it further.

Helpful Links

faq-wiring.aspx

Skyler R.

12/5/2022

@MikeL thank you for your feedback. I've diagnosed it as old bad wiring and ground. Will be rewiring it this weekend. Once again thanks for the response.

Mike L.

12/5/2022

Glad to help! Give us a holler if you need anything else!

Joe H.

12/4/2022

I have a 6x12 enclosed trailer that all the lights and signals work the way they should. When it's plugged into my 2018 f150 and press the brakes I get the trailer disconnected message. When I let off the brakes I get the trailer connected message. I have found that I have a ground on the brown lead of the wiring harness. I have traced the wiring throughout the trailer but can't seem to find any issues. Any ideas? Thanks

Mike L.

12/5/2022

Explain to me further what you mean about 'having a ground on the brown lead'.... I'll be happy to help through this, but need a little more info.

Justin

1/26/2023

@JoeH this is more of a common ford issue in my experience there is either corrosion or bad connection via the trucks 7 pin connector, i just replaced ours with one from the auto parts store, big metal clips holds the plug into bumper.

Mike L.

1/26/2023

That's a great idea. Check the connection between the tow package harness and the 7-way for green or white corrosion, and replace if necessary. We offer the OEM replacement as part # HM40975 .

Helpful Links

custom-fit-vehicle-wiring/hopkins/hm40975.html

Andrew H.

8/2/2022

Hi I have a f150 2018, every time I pull my travel trailer my drunk battery dies. Just finished a long trip during which I had my alternator changed but still ended up with the same problem. Any ideas what could be the problem?

David B.

8/3/2022

Well my friend something is draining your battery. Check the connection posts on the battery to make sure they are not corroded and have good connection. There could be excessive pull/demand on the battery that the alternator can't keep up with. Check your fuses, in some cases a fuse can actually cause an open circuit instead of breaking it or a parasitic drain. There is going to be a lot of troubleshooting involved. Also, the old battery may just have been "done" and need to be swapped out.

Helpful Links

article-categories.aspx?productgroup=battery-charger

question-334533.html

Cory E.

7/1/2022

I got a 1973 camper and the trailer plug is gone. Can't figure out the wiring for a new one. It has red green white black wires.

David B.

7/1/2022

Only way to figure it out is to get a circuit tester and troubleshoot it. Get a new connecter and wire it up. Then connect it to power and test the circuits out. Hit the blinkers and brakes to see what function works or doesn't then rewire as needed until you get the right function.

Helpful Links

faq-4-5-way-troubleshooting.aspx

faq-wiring-4-way.aspx

Koreyk

10/23/2022

@CoryE red passenger turn brake, green driver turn brake, black is running lights and white is ground. maybe

Dennis P.

6/30/2022

I work for a paving and excavating company, we have a 32’, dual axel, dovetail trailer w/ 8’ hydraulic lift ramps…the trailer gets pulled by a 2022 peterbilt 567 tri axel dump truck 7 pin connector…I would like to know the best way to set up so when the trailer is being towed it will charge, or at least maintain, the trailer battery for the ramps?? Thanks in advance!

David B.

7/1/2022

Best way is going to be adding a Redarc In-Vehicle BCDC Battery Charger - Single Input - DC to DC - 12V/24V - 12 Amp # RED96FR .

Helpful Links

tv-review-redarc-battery-charger-red96fr.aspx

Joey F.

5/3/2022

Helping my neighbor out. When he connects his trailers flat wire harness to his truck during the day everything works perfectly but come night time when his vehicle sensor comes on to turn on the headlights automatically his trailer lights goes out and stops working.

David B.

5/3/2022

What's up Joey? Let me link you to one of our expert answer pages that talks about a similar issue. I think this will help out. If this doesn't help let me know and we can start troubleshooting from there.

Helpful Links

faq-4-5-way-troubleshooting.aspx

question-96724.html

tv-review-draw-tite-circuit-tester-40376.aspx

Jason

11/27/2022

@DavidB. I kinda have that same problem. 2022 gmc sierra. Re done the wiring on the truck. Today it was still day light out. Finished securing the wires rehooked back up the trailer and now we have no power from the main plugin on the truck to the trailer do note went through with the test light and tested all fuses going to the trailer we have no power on any of the fuses but to let you know on the plugin for the truck we do have power on the battery but no power on any of the other prongs

Mike L.

12/1/2022

That's happening because he has the auto headlight option turned on. If you turn the headlights off and on manually, everything should work okay for you then.

See All (4) Replies to Joey F. ∨

John M.

4/19/2022

I just purchased a 2004 shadow master 6x12 enclosed single axle trailer. I have power at my connection on my truck but I get nothing lighting up on the trailer at all. the harness for the trailer ends up going inside the frame near the tounge. How to I figure out what's going on?

David B.

4/19/2022

Did you try yelling at it and kicking it? That helps me sometimes....Get a Hook Probe Circuit Tester # PTW2993 (or something like it) and start testing the wires. Hook up to power and start at the connector testing each wire and work your way back. Since the wire harness goes into the frame I would check all your ground points first before you dig into the actual wire harness. If you do NOT have a junction box I highly HIGHLY recommend installing one to make life easier for you in the future.

Helpful Links

faq-wiring-7-way.aspx

faq-wiring.aspx

tv-review-performance-tool-hook-probe-circuit-tester-ptw2993.aspx

Ben M.

4/10/2022

I installed self-adjusting brakes and when the tow vehicles brakes are activated I can hear a hum from the assembly (which I'm assuming is the magnet activating) but the brakes don't do anything. From an adjustment standpoint the brakes are making contact with the hub when not activated so I think their baseline adjustment is ok. Any thoughts on what I'm overlooking?

David B.

4/13/2022

You should barely hear a little scuff/scrape when you spin the wheel with no power to the brakes. Make sure the magnets are actually engaged when power is applied. Just because you hear a hum doesn't mean they are getting enough power to connect. I linked a couple help articles to walk you through testing the magnets and brakes.

Helpful Links

faq-adjust-trailer-brakes.aspx

faq-testing-trailer-brake-magnets-for-proper-function.aspx

Gary

10/5/2022

@BenM Im having same problem. Have seven way plug on truck. All lights work great but not brakes.

David B.

10/6/2022

See if this link helps you out Gary, let me know!

Helpful Links

question-36310.html

David B.

4/7/2022

2 trailers;both are wired w/4wire conn. I want to add 2" recv.on larger one and tow the 2nd. I need to run 4wire conn. from Ist to 2nd, How and what do I need to accomplish this? Thank you for your time and advice.

David B.

4/13/2022

First make sure you can tow your trailer legally like this. This circumstance will be considered triple towing and there are different rules and regulations surrounding it. All that legal stuff out of the way, I'd say look at # C13701 , then take a # 118001 and splice into your front trailers wires to make a connection. If you don't have LED lights you may draw to much power and won't be able to light everything up, just convert some lights into LEDs.

Mike R.

3/27/2022

I want to wire my trailer for tail, brake lights with left and right turn signals. The tail lights only have 2 wires and the wire I bought has 4 wires with flat plug in to truck. With only 2 wires on the tail light, what wires do I use of the 4 coming from the truck

Les D.

3/28/2022

@MikeR your trailer should have at least 4 wires. Green for right blinke/brake light. Yellow for left blinker/brake light. Brown for running lights. White for ground. I have attached a link that details all the trailer wiring and lighting. If you want to entirely replace your trailer wiring you can use the # 18252 kit with tester.

Helpful Links

faq-wiring.aspx

Mark B.

3/14/2022

We have a 7 pin harness on trailer. Most lights work ok but the left blinker only works when the right blinker is activated. Right doesn’t activate with left. Brake light is also inconsistent in working. Thoughts on where to start looking. This site and article is super helpful

Les D.

3/15/2022

The first go-to lighting problem solver is grounding. It causes the most problems and unexpected issues. At the 7-pin connector at the back of your vehicle you will find a white wire that comes off of the back of the connector and attaches to the back of your vehicle. Remove this connection and wire brush the connector lug and the metal attachment spot down to bare clean metal. The same for the trailer. Near the coupler where the 7-way connector and cable is you will find another white grounding lug. Clean and reinstall it as well. I have placed a link for troubleshooting trailer wiring below.

Helpful Links

faq-4-5-way-troubleshooting.aspx

Mark B.

3/15/2022

@LesD thank you !!

Brent G.

2/21/2022

I have a new Charmac cargo trailer that all exterior lights work properly, but the interior lights will only work if the truck is running??? I want them to be operable with the truck off and keys out out the ignition

Les D.

2/21/2022

Does your trailer have a flat 4-way connector, a round 7-way connector, or other? What about your truck?

Sharon S.

1/2/2022

I cannot find the fuse box and my electric is plugged in to a cord that works and it is not bringing the power in, Someone said check the fuse box

Les D.

1/3/2022

@SharonS what year/make/model of unit do you have?

Joe W.

12/29/2021

I have a 2017 Ford T150 van with 4/7 connector. When I have any trailer attached, the right turn signals flash really fast on the van, but the signals on the trailer don't work. Running lights, left turns, brakes, all work normal. Is this a ground? fuse? flasher plug? Everything works normal with no trailer attached.

Les D.

12/29/2021

The "hyper flashing" you are experiencing is usually due to LED lights on a trailer. The very low power they draw sometimes fool the vehicle into thinking there is a bulb out. This is easily fixed with load resistors. For load resistors, I recommend the LED Light Bulb Load-Resistors # DI34ZR. This will include 2 load resistors, one for each turn signal, and feature a durable construction.

Louis H.

12/14/2021

I have a 2011 toyota tacoma with a new T-one harness installed. I have a new 4 pin trailer harness with led lights installed on a 5x8 tilt trailer. Problem is everything works properly with my lights turned off on the truck but with them turned on: seems like the trailer brake lights are on constantly, no turn signals or variance when the brake is applied.

Les D.

12/15/2021

@LouisH these are classic signs of poor grounding or loose wires. I have attached an exhaustive article that will walk you through all of the possibilities. First I would check the white ground wire on the back of the trailer wiring harness. File the metal clean and shiny where it attaches. If you can connect your trailer to a different truck, this will be proof positive that the issue resides on the trailer side or truck side.

Helpful Links

faq-4-5-way-troubleshooting.aspx

Wendell S.

11/9/2021

I have a 1999 Chevy Silverado I was hooking up a 7 pin connector I have a light green wire coming from my wine out of my truck with no place to hook it to in the 7-pin where does the light green wire hook up to you

Les D.

11/12/2021

I have attached a link that illustrates trailer wiring and connector layouts. The green is usually the right side Stop/Turn signal wire. You can use a tester like # PTW2992 to check its function.

Helpful Links

faq-wiring.aspx

Matt

10/18/2021

Ok so I have my wires run and ready to connect on my trailer. I am putting in new LED lights and ran a flat 4 wire connector. I know I need to run the brown wire to my black wire, but where do I run the ground wire from the light? The ground wire is only about 8 inches long. And grounds to the tongue. What do I do with the other wire on the light?

Les D.

10/19/2021

@Matt The ground wire on your lights attaches to a grounded metal part of your trailer, typically within the 8 inches of wire that you have. Make sure you attach to a clear bare metal spot. Use a file to clean if necessary.

Mike S.

10/11/2021

Good advice This has been very helpful Thanks

Heather V.

10/8/2021

I have a 2011 F350 turbo diesel with a factory towing package. It has two 7-way plugs, one in the bed and one under the bumper. The trailer running/tail lights stopped working. When I checked the truck 7-way plug at the bumper, I had power at the pin but no trailer lights. Trailer service checked trailer said the lights all worked in the shop both with testing and connecting to another truck. The next thing the happened was the right trailer brake/turn light was dim, then it went out. I now only have the left brake/turn on the trailer. Please help me, I believe there are several fuses and at least two relays in the wiring harness. I am not sure where to start tracing this problem.

Les D.

10/19/2021

@HeatherV Let's verify your trailer service peoples findings. I guess one quick thing to try is plugging the trailer 7-pin connector into the bed outlet and see if you get any different performance compared to the bumper outlet. If there is a difference it could be a defective plug or poorly wired. It would not hurt to try a different truck, if you can, to make sure we know that the problem is truly on the trailer side or truck side. Lights not working or working dimly frequently point to grounding problems. On the trailer, just beyond the 7-pin is a white wire that will be screwed to the trailer frame. Take that off, and file the ring connector, and also file to clean bare metal where it attaches to the trailer then reattach and test. Same thing behind the 7-pin on the truck, there will be a white wire there connected to the truck frame that needs to be filed and reconnected. Test again. If still no power at the truck 7-pin we need to first check the fuses and then trace the power wires back to the source checking any inline fuses we find. Your owners manual will tell you which fuses in the fuse block are for trailer lighting. I have attached a document showing trailer wiring and which pins do which lights. Remember, you will need to have truck lights on to check running lights on the trailer, and flashers on to test turn signals. A tester like the # PTW2993 will make testing pins and circuits easier. See the attached video that shows how to use it.

Helpful Links

faq-wiring.aspx

tv-review-performance-tool-hook-probe-circuit-tester-ptw2993.aspx

Aj P.

9/28/2021

I got a older haulmark elite 2 race trailer. 7 pin plug. Hooked up everything. Bought new lights for it because I thought the old ones were bad because they didn’t work. All the wires under the trailer seem fine. Has a battery for electric breaks. Do I need a new battery for the brake lights and running lights to work. No lights or anything work on this trailer

Les D.

10/19/2021

The battery on your trailer could be for accessories inside your trailer like overhead lights, etc. A small battery on your trailer could also be for "breakway brakes" that only engage if your trailer comes loose from the tow vehicle while driving. The power for your electric axle brakes, running lights, brake lights and turn signals come from the tow vehicle. First determine if the problem is with your tow vehicle or the trailer. You will need a tester like the PTW2993 circuit tester. then consult the attached document for what to measure on each of the 7 pins on the connector. If you do not have power at the 7-pin then the problem is on the towing vehicle. Check the ground wire that is is connected to a clean bare metal place on the frame. Also file the ring connector to ensure a good connection. If that does not resolve your issue then you will need to trace the power wires to the power source checking any fuses you find along the way. Also check your owners manual for which fuses in the fuse block support the trailer lighting. If the problem is on the trailer side check for power at each of the lights. If you have power but no light, check the ground wire or the bulb. I suggest trying all of these options before installing any new lights.

Helpful Links

faq-wiring.aspx

Carlo N.

9/28/2021

I have a 28ft toy hauler, I put new brakes on &now I have a problem no brakes.

Les D.

10/19/2021

@CarloN It sounds like you forgot to reconnect the ground or power wires. Each electric brake has two wires. One wire for 12-volt brake power and one for ground. All 12 volt brake lines connect to each other and at the front connect to the 7-pin wiring on the braking line. All of the grounds connect to the grounded metal part of the trailer. The wires coming off the brakes have no polarity so you can use either for power or ground as long as all grounds come together and all power lines come together. I have attached a document on trailer wiring that has a good illustration of this. Let me know if this works for you.

Helpful Links

faq-wiring.aspx

Bill J.

9/26/2021

I have a new to me, 1995 2-axle, 2-horse WW trailer. It has the standard 7-pin connector and electric brakes. All the lighting work, however, the breaks become engaged as soon as the vehicle key is turned on. I've connected the trailer to two different vehicles with the same result. Somehow the breaks are getting voltage to engage even when the break petal is not pushed. Now i can't pull the trailer because the break system is always "on". Any thoughts on what's happening?

Les D.

10/19/2021

@BillJ I would start by testing the wires on the 7-pin connector on your tow vehicle. Use a # PTW2993 circuit tester. Most frequently when people have this issue we find that the electric brake line has been swapped with the 12-volt accessory line. The circuit tester will easily show you this. I attached a video that shows how to use this tester, and a document showing how trailer wiring at the 7-pin connector should be.

Helpful Links

faq-wiring.aspx

tv-review-performance-tool-hook-probe-circuit-tester-ptw2993.aspx

Mokp

9/23/2021

I have a big Tex utility trailer and with a seven plug connector and whatever it drives it appears that the brakes are on I looked at the wiring underneath and somebody has connected the ground to the power for the brakes what the hell is this a standard configuration or what can I do about it

Les D.

10/19/2021

I have attached a document that illustrates standard trailer wiring. It also includes a good illustration of the trailer break wiring. Electric trailer brakes each have two wires on them. One for ground and one for power. Brake wiring does not have any polarity, so either wire can be used for ground or 12-volt, as long as all 12 volt wires run to the brake wire on the trailer, and all the ground wires run to ground. Typically the ground wires attache to the trailer frame near the brakes, while all 12-volt wires are tied together and run to the 12-volt connection on the trailer. Finally, your 7-pin connectors have a blue wire for the trailer brakes. The also have a pin for 12-volt accessories. Make sure these have not inadvertently been swapped. If they were, the brakes would be on all the time.

Helpful Links

faq-wiring.aspx

Danny S.

9/1/2021

Hello. , I have a typical 2008 6x14 enclosed trailer , all the lights work great when plugged into my 2011 Tahoe but only 1 brake light and 1 blinker works when plugged into my 2001 Silverado 1500. , using the same adapter to each vehicle. Are these vehicles wired differently ?

Victoria B.

9/7/2021

@DannyS These vehicles would not be wired differently with factory wiring. Vehicle wiring is standard so that it will work with all kinds of trailers without the need for tons of different adapters. The colors used for wires on trailer wiring may vary, but trailer connectors are wired the same by function. I would use a circuit tester on your Silverado's trailer connector to make sure that all of the light functions are working correctly at the truck's connector. This will help you narrow down the issue. Since the trailer works correctly with your Tahoe, I am inclined to say that the issue is on the Silverado. It may be corrosion in the connector or one or more blown fuses.

Manny R.

8/20/2021

I have a 2014 GMC Yukon, 7 pin factory plug. I bought a trailer wired for 7 pin with an electric hitch. The electric hitch does not work on my truck but works on the truck the previous owner had, I believe it was a Toyota. Can someone point me in the right direction?

Victoria B.

8/26/2021

It is highly likely that the power wire on your Yukon need the final attachment made under the hood so that the 7-way actually has 12V power. I have linked a help article that talks about this issue and covers how to make the necessary connections in the "solutions" section.

Helpful Links

faq-tb-0007-2007-2009-gm-full-size-truck-brake-control.aspx

Darrell M.

8/19/2021

I connected a new 7-way to my truck for my trailer and brakes however now when everything seems to work but my running lights stay on after everything is off the keys off and they do not turn off I can unplug the main plug the tail lights will go off but if I turn the lights back on the tail light stay on again. And I'm using all standard bulbs no LEDs

Victoria B.

8/23/2021

I would check all of your grounds to make sure they are secured to bare, clean metal. Sometimes if a ground location has some corrosion or something like that it can cause a short and pull power though the connector. I would also check your trailer connectors to make sure they don't have any damage, corrosion, or bare wires touching that could be causing a short to draw power on the taillights even when the truck's lights are off. If everything seems to check out, a battery isolation solenoid may do the trick.

Darrell M.

8/24/2021

@VictoriaB Thanks, It ended up being the new 7-way. Rare but they are not always the best money can buy, even when it's a Hopkins. Of course now my brakes on the trailer are locked up when I connect my trailer to the truck.

Matt W.

8/17/2021

I have a travel trailer and a utility trailer and I am towing with a 2019 tundra. Both have a 7 way plug. Towing the travel trailer, everything is fine. Whenever I am towing my utility trailer it constantly shows the trailer comes disconnected. This is most annoying. I have traced it down to the trailer brake system, but was unable to figure out anything from there. I notice above it shows different wiring configs for RV and Utility. Could this be the issue? I have noticed it one other time when towing another utility trailer? Is there an adapter, that I can use to eleviate this issue?

Victoria B.

8/19/2021

7-Way Traditional and 7-Way RV-Style connectors are wired in the same configuration but use different wire colors to indicate wire function. If your trailers are wired traditional vs rv-style, this should not be causing your "trailer disconnected" issue. Have you checked your utility trailer's connector for signs of wear and/or corrosion? Sometimes these issues are cause by a weak connection at the trailer connectors and as you drive down the road the connection comes and goes. I would also check the wire connections at the rear of the trailer plug (if accessable) to make sure the brake wire isn't working its way out of the connection point. If you find the connector is clean, let me know and we can try and troubleshoot further from there.

Wayne F.

7/30/2021

I have a 2008 TAB trailer that has a 7 pin connector. When hooked up to a vehicle with 7 pins all lights work correctly. I have a 1994 Chevy pickup with 6 pin and a 2015 outback with a 4 pin. Using a 6 pin to 7 pin or a 4 pin to a 7 pin brake lights ok, left turn signal work ok. running lights ok. Right turn signal all lights are blinking on the trailer. What can I look for?

Victoria B.

8/4/2021

My first instinct is to check the light grounds. When there is a ground issue, the trailer lights can behave oddly, in ways that don't make sense. I think maybe when you're connected to your tow vehicle with the 7-way, the lights are getting a sufficient ground possibly through the 7-way connector. I'm thinking the two adapters don't provide the same ground connection and are possibly causing this issue. I would check the ground at the right-side lights that are acting up, as well as the trailer's main ground.

Fidel B.

7/19/2021

By screwing the connection box of my 7 pin wire under the clip of my fifth wheel m I crushed a wire and there was smoking, so I closed the master switch of the battery. The 7 pin cable was not connected after my pick up. My q question is it would be the wire of the brakes that I would have to pierce with the aim which would have caused a short circuit. Thank you for your good advice,

Jon G.

7/20/2021

While our charts show what the typical wire colors are for trailer wiring, there isn't a law saying they have to be that color so you'll just need to test each wire to see what function it carries.

Jim N.

7/6/2021

I have a 2019 GMC Seirra Denali and I bought a new car hauler. The problem is I bought it about 200 miles away and the left signal light dosen't work. Since it would cost more to haul it back than pay someone to repair it. I have checked all the connections I can find and checked the bulb all are fine. Any help will be appreciated.

Jon G.

7/8/2021

Have you checked the fuses in your pickup? Attached is a link to our helpful article about troubleshooting wiring that you can check out.

Helpful Links

faq-4-5-way-troubleshooting.aspx

6/16/2021

What a great article very informative. I do have a question. I am switch my old rv tail lights to a led tail light. Upon looking at the wiring it has 4 wires coming out hooked to old light. New light has 3 wires from partsam light. I am going to systematically test each to find out what works what. But does any of those effect my trailer brakes, like if I hook them up wrong? Because I’m going to have to combine 2 of the wires together so they can connect to one of the three wires? Right help!

Jon G.

6/22/2021

First just to clear the air, your trailer brakes are on a different circuit than your lights so you can rest easy there. When it comes to different amounts of wires what we normally see is that one of the lighting units uses the mounting hardware to ground while the other one used a wire. Testing your wires per function is the absolute best way to make sure you have everything hooked up correctly.

Plumberjohn

5/24/2021

I have a 1973 slide-in truck camper. I'm trying to connect the electrical pigtail from my 2002 Chevrolet Silverado. The slide-in truck camper had a 6 Pin round (male), and the truck has a 7 Blade round (male). Is there an adapter or cable to make this possible? I'm not able to determine what pin does what on the slide-in truck camper. Any advice is greatly appreciated! Thanks!

Jon G.

5/25/2021

You should be able to use something like part # 47549 for your application. With this adapter the middle pin is setup as the hot lead.

Clifford B.

5/23/2021

I have a 2009 Ford F 150 with the 7round plug and a 4 flat wire plug I can use either one just bought a new set of magnetic lights with red and orange lens and already have the led lights mounted in the trailer only all lights work when head lights on truck are turned but no brake or turn signals I have a 7 pin to flat 4 round connector why is it that the lights work but not the brake or turn signals

Jon G.

5/25/2021

Have you checked to see if you're getting a signal on those pins without the lights connected? It could be that you either need to replace some fuses in your truck or that you have a bad set of magnetic lights.

Gary S.

5/16/2021

I have a Wells Cargo Auto Hauler trailer. Originally in the black box that houses all the connections (located on the front tongue) there was a diode in-line with one of the wires. My friend borrowed the trailer, and somehow burnt out (melted!) the wiring. Now the back up lights on my 2006 Dodge Ram 3500 stay lit when I plug in the 7 blade connector. How can I fix this, or what part/wiring kit do I need? Much tanks.

Jon G.

5/17/2021

I would replace what you currently have with a completely new box like part # e99011 so that you can get rid of the bad wiring. I'm not sure what wire that diode is on but I would also try to figure that out and replace it with a higher-end diode like part # RM-690 if it was a single-light diode.

Jim S.

5/15/2021

I have a 2021 VW ID.4 which come pre-wired for 7 pin connections, while the kayak trailer on has only 4 pins. What solutions are there

Jon G.

5/17/2021

I would look into either using an adapter like part # TR20141 which just plugs into your 7-Way or by using a completely different connector like part # 30955 which plugs into your US Car Connector (when you unplug your current 7-Way from the back). This gives you both a 4-Way and a 7-Way so that you don't have to keep track of an adapter.

Jake W.

5/8/2021

the 2003 ford psd wire colors are not the same as you are claiming. at least on my truck. i know. im trying to rewire a new plug in right now. keep blowing fuses.

Jon G.

5/10/2021

The colors that we mention are just standard wire colors but they don't always match in real-world applications. As you've found in your situation you'll want to test the wires per function instead of just going by the color.

Shannon

5/5/2021

How can I run a 12v fuel pump into a 7 pin and control the power from a uplifter switch in the cab of my truck Ford F-250 super duty

Jon G.

5/6/2021

I'm not sure how you would make the connection to your uplifter switch and you would want to make sure that you have a circuit breaker or fuse to protect it, but what I would do is run 10 gauge wire # 10-1-1 from your uplifter switch back to the 12V power pin on your 7-Way which would be the pin in the 1 o'clock position .

Shannon

5/6/2021

@JonG ok thanks I’ll try it

Steve

5/3/2021

I have a 2020 G M C truck I wonder can I use the light wire to charge my battery to my power winch it a lawn mower battery ? If I turn my lights on while running ? That the flat 4 plug .

Jon G.

5/4/2021

The 12V power wire struggles enough to charge a battery with a 10 gauge wire so the smaller 16-18 gauge wire used for your trailer lights will not be nearly large enough to give your trailer battery a trickle charge. Your truck should have a 7-Way socket as well so all you should need to do is install a 7-Way on your trailer and route the power wire to your trailer battery. I recommend the kit # e99011 because it will help keep your wiring organized and make future repairs or modifications much easier.

Steve

5/4/2021

@JonG thank you

Jon G.

5/5/2021

@Steve You're welcome!

Ben

4/30/2021

Without turning the mini van on I have full lights on, brake, left and right work perfectly. New cable harness. I need to disconnect the trailer connector to kill the running lights. Any ideas

Jon G.

5/3/2021

It sounds like you have LED lights on your trailer. LED Lights are nice because they don't require as much power to operate but as a result sometimes they will light up dim when there is the smallest amount of power on those circuits. If you use a resistor like part # C57003 for a 7-Way setup or some that you install on the wiring directly, like part # DI34ZR , it should take care of your problem.

Bob C.

4/20/2021

Hi. What is the best way to add a third brake light on a camper shell mounted on a 2002 GMC Sonoma SLS? I have a junkyard rescue shell that does not have a third brake light and will mount an aftermarket LED but I am not sure if a hot wire is available. Just need advice from more knowledgeable folks

Jon G.

4/22/2021

Sometimes there will be provisions for 3rd brake light wiring somewhere along the frame but from the research I've done in the past it seems like there is no rhyme or reason as to which trucks have this wiring and which trucks don't. The best solution I have for you is to install the 3rd Brake Light Logic Module # PP20-702 . This is a very straightforward installation and will give you that brake signal that you're needing.

Edward R.

4/18/2021

Hi! I have a 2012 RAM 1500 quad cab which has the standard incandescent lights. I’m building an Wind Stream 24ft utility trailer with LED LIGHTS. Question is “Do I need to have a converter to control the return voltage to control and protect the fuse panel in the truck?”

Jon G.

4/20/2021

If you don't have the factory 7-Way and you're just wanting to install a 4-Way flat trailer connector for the trailer lights then I wouldn't say you HAVE to have a converter, but it does help to protect your truck so I do recommend using a wiring kit that comes with one like the part # 119178KIT .

Craig W.

4/16/2021

I need to wire a four flat to the back of my camp trailer in order to connect to small aluminum trailer which already has a four flat. Any advice on this project would be helpful.

Jon G.

4/20/2021

You can try to tie that into your current trailer wiring with a 4-Way flat like part # 18252 . One thing to be mindful of is that this will pull more power on those trailer light circuits so you might see problems there if there is too much power being pulled.

Gordon S.

12/11/2021

@JonG if you still need to finish this project, might I suggest you run a four wire flat extension from the front off the travel trailer to rear along the frame and connect the small aluminum trailer to it. Use a Y-splitter at the truck tailgate and power both trailers independently. I was unable to post a couple of photos for reference. Google 4 Way Flat Y-Splitter Plug and Play Adapter Extension and Trailer Wire Extension, 20ft, 4-Way 4-Pin Plug Flat 20’ Harness Extender Good luck.

Matt S.

4/2/2021

Is there a ASME, NEMA or other standard that controls the pin diameter and spacing of 4-flat plugs? I have several trailers with 4-flat plugs and the spacing and diameters, while similar, do not appear to be the same, which makes it difficult to plug into some and loose connections on others.

Jon G.

4/3/2021

I don't think there is a specific standard when it comes to the spacing and sizing for the 4-Way flat plugs - I think it's more of a "make your plug to fit like this so that it works with everyone else" sort of thing. You definitely aren't alone with this situation, which is why Hopkins came up with their Easy-Pull Harness that has a ring in the middle of the connector that makes it easier to remove when you need to. For a trailer end piece use part # HM48114 and for the vehicle end use part # HM48044 .

Butch

3/29/2021

I have a 2001 Ford f250 super duty truck, I just purchase a sure trac enclosed trailer and moved to Florida. All the lights work on the trailer however I cannot get the Interior dome lights to work. I watched a you tube video to where a man said that his Chevy truck did not have the fuses installed in the fuse box, can anyone tell me what fuses I need to check and have installed? Any help would be appreciated.

Jon G.

4/2/2021

You should be able to find this location in your copy of the owner's manual. When I looked online I believe the fuse you're looking for is in location 16 and is labeled as "Trailer Tow Battery Charge" and it sends back 12V power. You'll want to confirm this on your end too.

Steve

4/12/2021

@Butch My trailer dome lights only work when the truck running lights are on.

Willie J.

3/28/2021

Hey, I just brought a used Carry-On trailer with a 7way flat and it have three wires on the left side and two wires on right side running from the rear for clearance marker and tail lights . With only one oval LED fixture at rear on each side. Do I need a 5 to 4 converter? My truck is 2010 Ford F-150 with turn/brake is feed from the same wire.

Kef G.

4/1/2021

It sounds like your trailer has a 7-way blade, and your F-150 has a 4-way flat. What you need to do is upgrade your 4-way flat to a 7-way blade with part # ETBC7 . This will give you the 7-blade trailer connector you need.

Bill F.

3/25/2021

Need to go from 4 wire flat on motorcycle to 9 wire round on a can am motorcycle trailer. It is a 2018 Honda motorcycle.

Kef G.

3/25/2021

There aren't any 4-way to 9-pole adapters, so the best way to get this working is to splice a 4-way into your trailer and remove the 9-pole.

Drew M.

3/16/2021

I have 6 wires going into a 7 wire plug. None of the wires are blue and my electric brakes do not work. The only blue wire I see goes to a junction box on trailer w/black wire. How should I wire the plug? Should the black act as the blue wire? Very frustrating

Jon G.

3/18/2021

While this article shows industry standards, it isn't a hard and fast rule. It sounds like you'll need to test the functions of all of your wiring and make your connections per function instead of per color.

Richard H.

3/14/2021

I am rebuilding an old aluminum trailer and have purchased new replacement sidemarker lights. Because the metals react to each other and corrode, I have put a silicone gasket between the two metals. Will this cause a grounding issue? I have done the same with the new taillights. Thx!

Jon G.

3/15/2021

If the grounds for the lights are not able to make contact with the trailer frame then yes, that will cause issues. To try to avoid the corrosion you're talking about I would try to ground all of the lights to a main ground line and route that up to your trailer connector.

Dan O.

3/6/2021

Question, not sure if this is the correct location to ask a question. But here it is. I have a 1982 Sunline camper trailer. I replaced the standard bulbs with new LED tail and running lights. Their was green and white wires at running light locations. Here’s the issue, when the running lights are OFF the turn and stop lights work fine. When the running lights are ON the turn and STOP lights DO NOT work.

Jon G.

3/8/2021

Sounds like you either have a bad ground or short in your wiring. Check and make sure that all of your wiring (on both sides of the towing setup) is in good condition and that all of your grounds are secured to a clean, bare-metal surface. Attached is a link to a tiring troubleshooting article that you can check out.

Roger K.

4/10/2021

@DanO I also ran into a simular problem with my vehicle when I converted to LED lights. I found the problem to be that the vehicle had a negative switching system which does funky stuff to the lights. I wired in relays to convert the negative switching to positive switching now I am having no issues.

Emmanuel A.

3/2/2021

Hi there a have a small car dolly 7pins plug and the colors the my has is yellow Lt, white GD, green Rt but i am confused theres is one wire yellow/brown and green/brown i dont know what terminal are those TM or EB or AX. I need some help please. Thank you

Jon G.

3/4/2021

What you're going to need to do is apply 12V power to those wires and see what happens when you do that. Brown is typically used for running/tail lights so that might be where those wires need to go, but you also need to make sure that you have the stop light covered as well (which is typically on the same circuit as the turn signal). The one annoying thing about wiring is that there are typical colors but it isn't an industry standard that everyone has to follow. This means if something doesn't quite match up (like what you're experiencing) then we need to do the testing.

Dave H.

1/28/2021

I really don't like the Idea of "showing" electric trailer brake wire being grounded to the trailer axle. My axles move and is some what going to have a voltage drop when finding ground. My preferred method is to connect to the ground wire and keep the frame ground out of my schematics. By adding undetermined amount of resistance to the brakes you may end up with each wheel or at least each axle getting a different current flow and uneven braking. Thank you for having all this information quick and easy to find.

Gordon S.

12/11/2021

@DaveH I agree for the most part. Just rewired a small utility trailer with a tilt feature with LED lights. I ran a separate ground wire down each side of the frame for each marker light and taillight from the same point I grounded the connection at the tongue. This way it does not rely on a ground at the pivot point, the lights maintain maximum power constantly.

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