Troubleshooting Trailer Taillights that Don't Function Correctly When Headlights are On

Question:

I have a 2010 Honda CRV. I properly installed wiring harness #118427, and attached to my trailer. Everything initially worked fine. My trailer wiring got pinched and ripped off the white ground wire. The right side wires were also damaged on the trailer. I cut out damaged wires and spliced together. Right side would not work properly. The turn signal works only when lights on vehicle are off break lights do not work. When vehicle lights are turned on, nothing on right side of trailer works. Left side of trailer works with vehicle lights on or off. Vehicle lights all work properly. I completely rewired the trailer with new wires and harness. I have checked the fuses, and they seem to all be fine. Still wont work. Is there any way #118427 could be fried/needs to be replaced? Or do you know exactly which fuse numbers could be affect this?

asked by: Andrew F

Expert Reply:

It sounds like the problem is in the ground circuit. Any time we have seen taillight circuits stop working when headlights get turned on we know the problem is the ground circuit.

Since your ground wire got ripped off at one point I would make sure it is reconnected well. And you should make sure your taillight assemblies are grounded well to a clean metal surface. Some assemblies ground through the mounting hardware so you would want to make sure they are installed onto a clean metal surface. It may be necessary to run a jumper wire from the mounting hardware to an portion of the trailer frame if where the assemblies install is not an adequate ground.

I attached an FAQ on trailer wiring plus an FAQ on diagnosing 4-way installs that you may also find informative as well.

expert reply by: Jameson C