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


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


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



Are you able to include the troubleshooting link?



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.

Etrailer Expert

Mike L.


@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:



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

Etrailer Expert

Jameson C.


@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.



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

Les D.


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.



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

Les D.


Good luck to you - intermittent problems are the worst.
See All (5) Replies to Ray ∨

Dale K.


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.

Victoria B.


@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.

Chris J.


@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?

Les D.


@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.
See All (6) Replies to Dale K. ∨

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