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

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.

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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.

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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.

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Tommy

6/24/2024

@ChrisR if I'm getting my brake lights to work on my truck and I test the plug at the back of my truck and no lights light up in the plug is it a bad ground and if so if I had a bad ground with the brake lights on my truck not work

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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.

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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

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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.

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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!

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Jon G.

4/8/2021

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

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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

Tommy

6/24/2024

If the brake lights work on my truck but not on the trailer plug coming off my truck could it be a ground wouldn't the tail lights on my truck not working if it was the background

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Kevin C.

6/25/2024

@Tommy The tail lights and trailer connector signals are powered separately so the trailer connector could be malfunctioning but the tail lights will still operate normally. The ground is typically the first thing to check whenever you're facing a lighting issue. If this is a recent issue and the wiring was working before then it would likely be bad/weak ground, short in the wiring, blown fuse in your truck, or a bad converter if you have an aftermarket wire harness with one. Start by checking the trailer stop/turn fuses in your truck's fuse box. From there you can trace the wires of the harness and check the ground. If everything looks fine and the wiring harness has a converter then check for the signal before the converter and then after it. If you're getting the signal before the converter but not after then the converter is bad. If this is a factory 7-way then you wouldn't have a converter and wouldn't need to go looking for it.

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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…

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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…

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Answer 3

That's a good question, and the answer is that your current 5.30-12 tires are not safe for traveling at highway speeds. What you likely have on your trailer now is a bias ply tire, which is not good for highway use because they are stiffer and…

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Answer 4

The most likely cause for the turn signals not to work when the running lights are on with your trailer is a bad or weak ground. It's very possible that a weak ground connection can be just strong enough to allow sufficient current for some…

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Answer 5

Even though I cannot comment specifically on the grease you used because I am not familiar with it, I can tell you the best grease for trailer bearings is a a grease with a rating of GC-LB, which just means it is made to withstand very high…

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Answer 6

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…

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Answer 7

I looked in the owners manual for your 2013 Chevrolet Suburban and it can be flat towed or dolly towed, depending on if it's 2 or 4 wheel drive, and if it has a single or two speed transfer case. If you suburban is 2wd or has a single speed…

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Answer 8

A vehicle's towing capacity depends on the entire complement of factory equipment installed on it. The best place to confirm this is the owner's manual. I checked an online edition of the manual for the 2014 Jeep Grand Cherokee Limited with…

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Answer 9

There are two different sets of tail lights on a 2013 Volvo XC70, a pair in the quarter panel at chest height and a pair in the lower bumper at knee height. I took a look at all the trailer wiring harnesses for a 2013 Volvo XC70 (Curt T-Connector…

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Answer 10

Trailer wiring harnesses for your 2011 Volvo XC70 use powered converters to draw the power for the trailer's wiring. This prevents the taillights of your Volvo from having to power the trailer wiring. The Hopkins kit part #HM11143735 that fits…

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Answer 11

On a 7-Way and 4-Way, the brake light function is on the same wire as the turn signals. So if your turn signals are working, then the connection is made, there is just a problem that is not allowing the brake lights to function. Most likely, there is…

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Answer 12

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, inspect…

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All Trailer Lights Work Fine Except Brake Lights Will Not Work

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