Trailer Running Lights Do Not Work but Brake Lights and Turn Signals Do Work

Question

Question:

Blinkers and break lights work but tail/running lights dont. Truck tail lights are working. Is it a fuse or is it wiring?

asked by: Joan C

0

Expert Reply:

It could be a tow package fuse on the vehicle. Use the owners manual to find the locations of fuses/relays related to the tow package wiring to check them and replace as needed.

If the issue is not a fuse or relay then you can test the vehicle side trailer connector using a circuit tester such as # PTW2993. Turn the vehicle headlights on and use the circuit tester to test the pins on the connector at the back. If there is no power on the running light pin then there is a break or loose connection somewhere between the connector and where it terminates at the front of the vehicle that you will need to track down.

If everything checks out on the vehicle then the issue is on the trailer. Make sure the trailer connector is clean and free of corrosion inside and out. The main trailer connector ground and the grounds for all of the lights need to be attached to clean and corrosion free bare metal surfaces.

If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H

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Anthony A.

4/14/2024

I have brake, turn signals and backup lights in my trailer just no running lights. The fuse is good on the truck and I nothing wrong with the plug. What else could I check?

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David A.

1/10/2021

Hello I have a trailer where the running lights don’t turn on but they flash when I lock my truck I’ve tested fuses checked the plug connections any ideas?

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Jon G.

1/14/2021

Michael gave a few more tips on testing the vehicle and trailer side of your setup. I'd try using his troubleshooting tips so we can figure out where the problem is at.

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Garry R.

3/21/2021

@JonG I have pretty well the same issue. Turn signals and brake lights work, running lights don’t. But brake lights don’t work with the running lights turned on.

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Kef G.

3/24/2021

@GarryR You'll need to check the wires on the vehicle side and trailer side and look for any pinch points or corrosion. If you find any, replace the wires. Also, be sure to check the ground wires' connection points since any rust or corrosion there will cause some things to not work.

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See All (8) Replies to David A. ∨

Kirby P.

9/8/2020

I a skeeter trailer, and the turn signals, break lights, back-up lights work, but the running lights stopped working. where should i start first looking for the problem?

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Jon G.

9/8/2020

@KirbyP Sounds like you have the same issue as Joan did with her wiring when she asked the initial question. You're going to want to follow the same steps that Michael highlighted on this answer page.

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Smarty P.

3/9/2021

Experts? There is only one ground pin regardless of which connector you have. If it was a ground issue, no lights would work,

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Jon G.

3/11/2021

@SmartyP Hate to break it to you but each light has it's own ground most of the time. Sometimes people will run all of their grounds together on 1 wire and connect that to the trailer connector, but a lot of times each light will either ground through the mounting hardware or by using a self-tapping screw and a ring terminal on the ground wire. If you don't believe me just take a few minutes to meander through our trailer lights selection (which I've linked for you) and check out the descriptions.

Helpful Links

dept-pg-trailer_lights.aspx

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Will D.

9/8/2020

Was rewiring my trailer last night and everything was working perfectly. I was wiring the trailer hot as I had the truck on and trailer connected as I was doing the wiring. On the last light I let the positive touch the trailer and I heard a sizzling noise and ban my running lights stopped working. I checked the truck for any blown fuses and nothing. My blinkers work and brake lights. I checked the trailer connection at the truck and my running lights are not working. Could I have messed up the harness?

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Jon G.

9/8/2020

@WillD If you heard a physical noise coming from your trailer lights/wiring then you very well could have damaged something with the harness. You're going to have to trace the wiring all the way from the connector to your lights and even check that your lights are still good as it could literally be anything on that circuit.

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Philipp

9/6/2020

I have a 2015 Dodge Grand Caravan that I had the dealership i bought it from brand new,install a mopar factory trailer wiring harness on. Left and right signals work and brake lights but No Running Lights. I checked owners manual for fuse location and there are no fuses in there. I think when they installed it, they spliced all the connections. I couldn't find any in-line fuses either

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Jon G.

9/8/2020

If your trailer wiring harness isn't working properly and there aren't any dedicated fuses for it then I'd reach out to the dealer who installed it and have them fix what's wrong. If you're wanting to look into this on your end then you'll want to check out the wire used for the running light circuit and see how it was installed to make sure it's still securely connected.

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Rob

3/21/2022

@Philipp I have the exact same problem and have a model from the same parent company (2015 Jeep cherokee) and was wondering if you found out it might be a Mopar flaw?

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Doug M.

7/11/2020

On my 2018 Ram 1500 crew Ref: my boat trailer All my truck lights work but on the boat trailer only the driver side running light and blinker work, nothing works on passenger side trailer (and the boat and trailer are only one month old)

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Chris R.

7/16/2020

I would definitely start by testing the trailer connector on your Ram 1500. See if you are getting power on the passenger side turn/brake signal pin. If so, then the issue is on the trailer side. Since you mentioned that the driver side running lights work - I suspect the problem is likely on the trailer anyway. Make sure the main harness ground is still securely attached to clean bare metal and do the same for each of the individual trailer light assemblies.

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Doug M.

7/16/2020

@ChrisR

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Scott

5/19/2020

Hi there. Having a strange issue with my trailer lights. Brake and turn singles work but not my running lights within the brake, turn and running bulb. All other running lights work around the trailer. What’s weird is I have 12.4 volts going to all pins on the plug and yet the running lights still don’t work? The light itself is a single bulb light so not a blown bulb. Any ideas would be greatly appreciated. Thanks so much.

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Chris R.

5/22/2020

That IS a bit strange. Are these new trailer light assemblies (have they ever worked properly with the running lights)? I would start by checking their grounds - whether they ground through a dedicated wire or through their mounting hardware. Make sure they're securely attached to a clean, bare metal surface. Let me know what you find and we'll keep troubleshooting.

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Doug M.

7/16/2020

@ChrisR thank you for the info Chris, i actually found out that i had a blown fuse, i found that the left side trailer lights have a fuse and the right side trailer lights have their own fuse so when i changed the fuse for the left side the lights worked fine

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Chris R.

7/21/2020

@DougM Awesome!

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Answer 1

The 4-way on your trailer is what&amp;amp;#39;s known as a wishbone connector like part #A35W42B. Two of the wires are the running light circuit which is a little easier to install since you can run one down each side of the trailer. This…

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Answer 2

This could certainly be a grounding issue. When a circuit does not have a sufficient ground, it can cause many different issues. If possible, I recommend checking all of the grounds for your trailer taillights. You will want to make sure the ground…

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Answer 3

You will first want to check the fuses on your tow vehicle. Some vehicles could have fuses for operating the turn signals and brake lights of a towing package. You will want to check if they are installed and working properly. The next thing is to…

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Answer 4

To determine where the problem is first disconnect the trailer from the tow vehicle. Use a circuit tester such as #PTW2993 or a meter if you have one to test the vehicle side trailer connector while the head lights are on. If there is power on the…

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Answer 5

It sounds like there is a short circuit that is overloading the running light circuit in the tow package wiring on your tow vehicle. The most likely culprit is a dirty or corroded trailer connector on the vehicle or trailer if not both. The first…

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Answer 6

You have it right so far, the 4-way connector is just as you have stated. Remember that Yellow has a L in it so that is the left side brake/turn signal and green has a R in it so that is the right side brake/turn signal. The colors for wiring a…

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Answer 7

For your 2024 Nissan Frontier I recommend the etrailer Trailer Hitch Receiver #e98869. This is a Class III hitch with a 2&amp;quot; receiver and a max gross trailer/tongue weight of 5,000/500 lbs. This hitch also features a matte black…

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Answer 8

Since the signal and brake lights are working but the taillights are not, it sounds like you may be experiencing a ground issue. A weak ground can be just strong enough to provide some of the lighting functions but not all of them. If a ground…

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Answer 9

Your brake lights and turn signals for each side are on one circuit. The left side turn signal and brake light is generally the yellow wire going into your trailer connector. The first thing to do is check the fuses on your tow vehicle. Next,…

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Answer 10

Since your trailer is brand new I suggest a visit to the selling dealer or to another authorized service/repair center. Small parts such as light lenses are easy to replace and inexpensive, but troubleshooting the blown fuse problem is not. Finding…

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Answer 11

The number 15 fuse in the engine bay fuse box is responsible for the trailer parking lamps. For future reference, the owner&amp;#39;s manual will tell you where all the fuses are located and what they do.

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Answer 12

The first thing I would check is the trailer wiring running light fuse located in the power distribution box under the hood. Once the fuse box is located check the legend on the lid to determine the correct fuse to check. Blown running light fuses…

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Trailer Running Lights Do Not Work but Brake Lights and Turn Signals Do Work

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