All Trailer Lights Work Fine Except Brake Lights Will Not Work

Question

Question:

Everything works but the brake lights, what did I do wrong? I doubled up the white ground, put brown on Brown, green on green, and yellow on yellow but brake light fail to work. Any suggestions? Thank you.

asked by: Rob C

1

Helpful Expert Reply:

On a trailer the brake lights and turn signals operate on the same wire/bulb. So, it is odd when the turn signals work, but the brake lights don't. There are 3 possible causes for this that are more likely than any of the other possible causes.

First there could be a problem on the vehicle side. Use a circuit tester such as # PTW2993 to test the vehicle side trailer connector while someone steps on the brakes in the tow vehicle. If there is no power on any of the pins for this test then there is likely a blown or missing tow package, stop light, or CHMSL fuse on the vehicle.

If there is power, then the issue is on the trailer. A bad ground can cause this problem. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also 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.

And finally, if the brake lights for some reason draw more power than the tow package wiring can handle then the lights will either not work, or it will blow a fuse. If they are drawing too much power, then switching to LED lights will solve that problem because they draw a fraction of the power compared to incandescent lights.

I have included a link to our help article on troubleshooting wiring for you.

expert reply by: Michael H

1

Allen

8/5/2020

Have trailer isolation Honda goldwing 2016. Isolater is put out by electricalconnection. All lights work including flashers but no brake lights tested 5 pin plug at pigtail on bike. Blinkers flashers running lights all work but brake. Did I do something wrong?

Reply

Chris R.

8/14/2020

I'm assuming your Gold Wing has separate wiring since that's pretty standard for motorcycles, which means the brake and turn signal get sent along separate circuits. Unless you're pulling a trailer designed specifically for motorcycles, these circuits will be combined on the trailer side. So somewhere in-line before the 5-Way you'll need to add a converter like # RM-732 that you wire to the turn and brake light wires on the bike. If this isn't the issue just let me know and we can look at other solutions.

Reply

Dave D.

7/8/2020

I have a 1993 Colman/Fleetwood pop-up. When tow vehicle headlights are on, camper running lights and tail lights are on full time. No brake or turn signal lights. When headlights are off, I now have brake and turn signal lights. Bulbs are basic double pole. (1157) Is this right? Doesn't seem to safe for night driving??

Reply

Chris R.

7/13/2020

You should still get trailer turn and brake signals when you have the headlights on in the tow vehicle. I'm thinking you might have a weak ground on the main harness. Check to make sure the ground wires on both the tow vehicle and camper are still securely attached to clean, bare metal surfaces. Let me know if this does not resolve the issue.

Reply

Sam

4/8/2021

@ChrisR Was this ever resolved? I'm having a similar issue. Thank you!

Reply

Jon G.

4/8/2021

@Sam I think that would be a question better directed at @DaveD.

Reply

Jessie E.

6/1/2020

I bought a magnetic trailer light kit so I didn't have to wire anything and all the lights work except the breaks I've tested my 4 way and it says everything is working but the lights will not light up when I push the brakes

Reply

Chris R.

6/4/2020

It's always strange when just the brake lights or just the turn signals don't work since they are sent along the same circuit on trailer wiring. Is the magnetic kit simply hooked up to a 4-Way on your tow vehicle? If so, and you've verified that you're getting power on the 4-Way with the brake pedal, I have to think the issue is with the lights themselves and they may need to be replaced. There's unfortunately not much troubleshooting you can do otherwise.

Reply

Carl B.

5/10/2020

I read the above reply by Michael H and followed his suggestions. I sincerely appreciate his insight and mentioning a possible tilt bed because that never crossed my mind although it was exactly the issue with my trailer. Problem resolved. Thank you Mr. Michael.

Reply

Jake W.

4/11/2020

Working on a stock trailer. I have all lights but brake lights, the brakes work and all just the brake lights dont work. I have power at the plug on the truck.

Reply

Chris R.

4/13/2020

Since you tested the truck connector you at least know the problem is somewhere on the trailer. The brake and turn signals are sent along the same circuit, so the fact that just the brake isn't working leads me to think a weak ground is the culprit. Make sure your main harness ground is securely connected to clean, bare metal - and do the same with the individual light assemblies themselves. Let me know what you find and we'll go from there.

Reply

Jeff W.

2/25/2021

@ChrisR I just wanted to say thanks for posting all the above. I was able to solve my problem of all my lights working except the one break light. Turns out it was a poor ground at the trailer. Thanks again.

Reply

Answer 1

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…

view full answer...

Answer 2

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…

view full answer...

Answer 3

First, we need to figure out if the problem is on your 2004 Chevy Silverado or on the trailer. To do that disconnect the trailer and we can focus on the truck side trailer connector. Since you think it may be a ground issue you can use a circuit…

view full answer...

Answer 4

Most trailer wiring problems are the result of a bad ground. What I would do is start with the connectors. Maker sure the connectors on both the trailer side and vehicle side are free of dirt and corrosion and that they are properly grounded. Next,…

view full answer...

Answer 5

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,…

view full answer...

Answer 6

On both a 7-Way and 4-Way trailer connector the brake lights and turn signals are on the same circuit so it is strange that the brake lights aren&#39;t working. But, brake lights draw more constant power than the running lights or the turn…

view full answer...

Answer 7

If your trailer has separate turn signals from the brake lights and you want them to remain that way, you will need to use a special converter. On the trailer side, behind the 7-Way, you will attach the Vehicle to Vehicle Taillight Converter,…

view full answer...

Answer 8

Thank you for all of the details in your question. It looks like you have a faulty ground or some corrosion in one of your connectors. On a trailer the functions for your turn signals are also tied into the brake lights so if your right turn signal…

view full answer...

Answer 9

What you are describing is normally the result one 1 of 3 issues: First, there could be some corrosion in or on the connectors on the vehicle or trailer side or both. Second there could be a bad ground. Bad grounds can cause all sorts of bizarre…

view full answer...

Answer 10

The best base plate kit for your 2021 Willy&#39;s Jeep Gladiator is going to be the Roadmaster Direct-Connect Base Plate Kit item #RM-521453-5. This base plate kit has a concealed design that creates a factory look when you remove the arms.…

view full answer...

Answer 11

If you want to hardwire in a trailer connector to your 1998 Toyota Tacoma then you can use #HM48925. It is just more work though when you could use a harness that plugs in line with the vehicle tail light wiring such as #HM43315. But it is totally…

view full answer...

Answer 12

Whether or not you can flat tow with a Jeep bumper is really up to the manufacturers testing; some of the big names like MetalCloak or Poison Spyder have bumpers with D-ring attachments that can be used for flat towing connections. This is great…

view full answer...