Troubleshooting Running Lights That Only work on One Side of Trailer

Updated 04/26/2018 | Published 04/25/2018

Question:

I have brake and turn and running lights on one side of trailer and only brake and turn on the other side, no running light. Any ideas?

asked by: Michael B

Helpful Expert Reply:

It sounds like you have a short or some bad wiring on one side of your trailer. Since everything is working properly on one side you know that your tow vehicle is sending the signal and your trailer is receiving it.

Start off by checking the grounds on your trailer. Make sure that they are secure and connected to a clean, bare-metal surface. Next you want to inspect the wiring on your trailer. Typically, the running lights are on a brown wire, but since trailers can sometimes have different wire colors it is best to find the wire that is connected to your running lights and follow it all the way up to your trailer connector.

If everything looks good, you can then try using a circuit tester like part # PTW2993 and utilize the probe to determine where the signal drops off of that circuit and replace the wiring as necessary.

I have linked a helpful article on troubleshooting wiring that you can also check out.

expert reply by: Jon G