Working Running Lights, But No Turn Signals or Brake Lights On Trailer

Question

Question:

Why do I have working trailer lights, but not blinkers or brake lights?? Thanks...

asked by: John

0

Expert Reply:

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 make sure the wires on the trailer plug is wired properly to the trailer. If you have a 4-Way connector on the trailer the white wire is for ground, the green wire for right turn and brake, yellow wire for left turn and brake, and the brown wire is for running lights. I am including a link to a FAQ page on trailer wiring.

If the wiring is all correct then you will need to check the trailer connector on the vehicle and trailer for a ground connection issue, or a short on the tail light circuit on the trailer. Open them up and make sure there is no white or green corrosion causing an issue inside the connectors. If so clean them out or replace the connectors with new ones.

If the problem is not found in the connectors, you will need to follow the trailer wiring and check all of the grounds for all of the lights and the trailer connector. Make sure each light is grounded to the trailer frame and that the connection to the trailer frame is free of rust, paint and corrosion. Other lights like running lights down the side of the trailer may have a separate ground wire or they may be grounded through the mounting hardware so you will need to check each of these lights.

While you are checking all of the ground connections, it is a good idea to look at all of the wiring and check for pinched cut or frayed wires that could be causing your issue, or could cause an issue in the future.

I am including a link to a troubleshooting video that should help you with locating the problem on your trailer.

expert reply by: Jeff D

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John M.

4/21/2020

Definitely check all of the vehicle fuses first!

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Chris R.

4/23/2020

Absolutely!

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Bradley

4/17/2021

@ChrisR My trailer lights all work. My break lights and turn signals work with out trailer lights on. But. Break and turn signals stop working g when trailer lights (vehicle lights) are turned on. Help please.

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Jon G.

4/21/2021

@Bradley It sounds like you may have an insufficient ground on the vehicle or trailer side, or that the harness is overloaded when you turn the headlights on. Attached is an article you can check out that goes over some solutions for you. You'll want to reference methods 1, 3, 4, and 5.

Helpful Links

faq-4-5-way-troubleshooting.aspx

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Tom M.

7/3/2020

My driver side blinker works fine . My passenger side light won’t blink . Just wondering what you might check?

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Chris R.

7/8/2020

I would start by testing the connector on your tow vehicle with a circuit tester. Test the turn/brake light pin when you have the blinkers on to see if you get pulsing power. If not, then you at least know the issue is on vehicle (if you do, then the problem is somewhere on the trailer). On the tow vehicle check for any blown fuses under the hood if you have factory tow package, inspect the connector for any debris/corrosion that needs to be cleaned out, and make sure the harness ground is securely attached to the frame. On the trailer side I would start with the passenger side light assembly itself - make sure it's still properly grounded and the bulb is not bad.

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John

6/14/2024

@ChrisR, I bought new trailer tail lights. They are stop,tail, and blinker lights. I wired everything up and they just act as tail lights. No blinker or brake indication. All grounds are good that I can see.

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Kevin C.

6/14/2024

@John If only the running light signal is coming through then you either have the lights wired to the trailer wire harness incorrectly or your tow vehicle isn't sending any signal through to the trailer besides just the running lights. I would start by checking the trailer connector on the tow vehicle with a probe tester # PTW2993. If the signal is coming through there then you can check the wiring on the trailer checking the wires every so often to see where the signal stops.

Helpful Links

faq-4-5-way-troubleshooting.aspx

faq-wiring-4-way.aspx

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Gary B.

7/19/2020

Driver side turn signal and brake does not work on utility trailer. All other lights on trailer work. The yellow wire (signal and brake) measures 0 Ohms went tested with jumper wire from trailer connector to light fixture. When truck is connected to two other of my trailers all lights work on both driver and passenger side. What is my problem?

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Chris R.

7/24/2020

We at least know the issue is on the trailer. I would check the driver's side light assembly itself and make sure it's still properly grounded to clean, bare metal - whether it's done with a dedicated wire or through its mounting hardware. Let me know if this doesn't resolve the issue.

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Chelsea

7/29/2020

My passenger side light keeps coming on and off and when it is on, it will not signal or flash with my hazards. I’ve checked all of the wires and they’re all put together the way they should be/nothing loose. I also went and bought a new bulb just in case that was the issue but, of course, it wasn’t. What am I missing??

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Jon G.

8/6/2020

Sounds like you have a good ol' fashioned ground problem. Check all of the grounds for your lights on that circuit and make sure that they are all secured and free of any damage, rust, or corrosion. If this doesn't fix it let me know.

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Dale K.

11/1/2021

All lights and turn signals work until headlights/running lights are turned on then left turn signal does not work. If running lights/headlights are off then the left turn signal works properly. Right turn signal works properly.

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Victoria B.

11/2/2021

@DaleK When an odd sort of issue like this presents itself it is almost always an issue with the ground. Since the signal light works when the headlights are off, but not when they are on, it sounds like the ground is too weak to take the full power of both the running light and turn signal. Check your ground to make sure it is secure and doesn't have any dirt or corrosion preventing it from making a solid connection. Start with that and if it doesn't give you a solution, let us know and we can go from there.

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Chris J.

11/30/2021

@VictoriaB This is my issue, I have replaced the ground wire, put a new connector on it, put dielectric grease on the connection and it still has this issue. Turn signals work properly until the headlights or running lights on my truck are on then no blinking. Any more troubleshooting ideas?

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Les D.

12/1/2021

@DaleK First, when I have a customer send in a question I nearly always think it is about a trailer. Your question does not define if you are talking about a signals problem on your vehicle or on a trailer. If this is about a vehicle, please let us know what year/make/model it is. However, if this is about a trailer then I concur with @VictoriaB that this sort of issue is nearly always ground related. Let me expand on her comments. I would look at the ground connection where the white wire comes off of the back of the connector on the truck rear bumper. This will be connected to a grounded part of the truck. I would remove this connection and file the metal until shiny, and also file the connector on the end of the wire likewise. I would then then check the wiring harness from the trailer. It too will have a white wire grounding to the trailer frame. File that connection and connector clean. Finally I would also note that most trailer lights have a 12 volt signal connection, then the other wire from the light grounds to the trailer frame. I would check those grounds as well. I would also check the connector on the trailer wiring harness to see that none of the wires are pulled loose. Particularly the yellow wire that carries the left side signal light.

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Ray

11/3/2021

Not the first time this happened. All brake lights and turn signals work fine. After a while the turn signals and flashers stop working on both the vehicle (06 Ford Escape Brake lights and tail lights are working. I unplugged the trailer vehicle flashers and signals still not working, waited about an hour vehicle flashers and turn signals return to normal, I am stymied please help

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Les D.

11/5/2021

Not the first time this happened. All brake lights and turn signals work fine. After a while the turn signals and flashers stop working on both the vehicle (06 Ford Escape Brake lights and tail lights are working. I unplugged the trailer vehicle flashers and signals still not working, waited about an hour vehicle flashers and turn signals return to normal, I am stymied please help Lets determine if the problem is with the tow vehicle or the trailer. First, I assume then when you are driving your vehicle around WITHOUT a trailer that the lights work perfectly. If that is the case, lets move on to the towing electrical connection on the bumper of your vehicle. Use a tester like the Performance Tools # PTW2992 to check all the connections on your connector. While you are there, check the back of the connector for stressed or loose wires. Fix any problems that you find. Also see there on the back of the connector there is a white wire that runs from the connector to a metal grounding spot on the frame. Remove this connection and file the connection point to shinny metal, and do the same with the ring connector that attached there. This is the ground wire, and a dirty connection can cause all kinds of problems. If this all checks out we can move to the trailer. Use the same process of checking the electrical connector, the wires leading up to it and the trailer frame ground, like you found on your vehicle. If this all checks out then you will need to trace the wires to your tail lights. Watch for any crimped, cut, or worn wires and replace an necessary Watch for wire connectors that may be corroded inside. Keep in mind that your lights probably only have one wire for power and bolt to the trailer metal frame for their ground. Clean all grounding locations. I have attached a link to a document that will show you how trailers are wired. In that your issue is only intermittent, this will be difficult to work out. My best guess is a wiring connection on the grounds since you are having issues on two different circuits/wires at the same time.

Helpful Links

faq-wiring.aspx

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Ray

11/5/2021

@LesD wow thanks for getting back so quickly this will be my new weekend project, I will let you know

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Les D.

11/9/2021

Good luck to you - intermittent problems are the worst.

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Jerry

2/29/2024

All fuses are good I have only running lights on my 2001 ford f150 trailor lights

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Jameson C.

3/4/2024

@Jerry Have you tried cleaning the pins of the 7-way? Typically its corrosion that causes this problem. Also check the wiring that runs to the back of the 7-way looking for any issues like cut or exposed wire and fix as needed.

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Carol

3/10/2024

Where is the video regarding the trailer lights rear turns/emergency/backup not working...will one bulb out cause the issue? Also, we would like to replace with LED....btw, Running lights along the top work.

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Mike L.

3/12/2024

@Carol We don't have a video, but there is a troubleshooting article that I'll link for you. Having one bulb out shouldn't cause the turn signals and reverse laps to malfunction. As a first step, you'll want to determine whether the problem lies in the tow vehicle wiring or the trailer wiring. The easiest way to figure that out is to try that trailer with a different vehicle and/or try your vehicle with a different trailer. If that isn't possible, use a circuit tester on the pins of the trailer connector on the vehicle while each trailer lighting function is activated. If all the pins test okay, then the problem is in the trailer wiring. If they don't, the problem is on the vehicle side, with a wiring problem or blown fuse being two common culprits. Also, make sure the pins/sockets on the trailer connector aren't dirty or corroded. Here's some articles that will be helpful: https://www.etrailer.com/faq-wiring.aspx https://www.etrailer.com/faq-4-5-way-troubleshooting.aspx

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Rob

5/7/2024

Are you able to include the troubleshooting link?

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Ray T.

11/18/2024

I have working running lights and brake and turn signal on the right side of my trailer but no turn signal or brake lights on the left side.

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Robin H.

11/18/2024

@RayT with only half of them working it sounds like the there may be a short in the wiring. Check your brake/turn signal wire for power on that side of the trailer. It could also be a bad connector or a bad ground. If you don't have power right after the connector but have power on the vehicle side I would replace it with # HM48192. Otherwise trace your way back and repair the short when you find it.

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Cooper

6/7/2025

I have a problem with my trailer lights the running lights work but the blinkers and the brake lights won’t work. The brakes and blinkers worked the first when I didn’t hook it up to the ball but as soon as I put it on the ball the brakes and blinkers stopped working completely.

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Jesse M.

6/9/2025

@Cooper That is a bit bizarre but there must be a short somewhere so when you are putting the trailer on the ball it is completing a circuit and causing things to short out. Check the trailer and vehicle wiring for any damaged or cracked wire that may be causing a short.

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Answer 1

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 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

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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Answer 4

This sounds like a ground problem on the right side. The turn signal not working makes sense because with the brake lights, there is a constant signal coming through which is enough to make the lights illuminate on both sides like they should. But…

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Answer 5

Trailers use a combined wiring system meaning the brake lights and turn signals are on the same circuits. Since the brake lights are working on the trailer, and because you have tested the vehicle wiring and it is working properly, there is most…

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Answer 6

First, disconnect the trailer from the tow vehicle so you can check the vehicle side connector. Using a circuit tester like part #PTW2993, test the functions of the connector; specifically check the right turn/brake, to make sure the signal is making…

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Answer 7

This sounds like a ground issue. 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. Make sure that the vehicle side and…

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Answer 8

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…

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Answer 9

You should be getting 12 volts on the running light circuit when the running lights are turned on. If not, the problem is either in the connector or upstream from there. The first thing you should check is the trailer connector on your towing…

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Answer 10

It sounds like you either have a blown fuse or a short on the right side turn light and brake light circuit. First, I recommend checking the trailer wire connector on the vehicle. You can use a circuit tester, like #PTW2993, to test that power is…

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Answer 11

The 4-way on your trailer is what'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 way you don't…

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Answer 12

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, I…

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