Troubleshooting Trailer Taillights that Stop Working When Headlights are On

Question:

I have the same question as Matt when the running lights are on the brake lights and turn signals dont work wiring on truck conector is fine

asked by: Danny P

Expert Reply:

Your main problem is an insufficient ground for the trailer wiring. Try improving the connection of the main ground wire of the trailer wiring harness. Make sure it is attached to a clean metal surface. Or you can run all of the trailer wires back to the main ground. This is actually the ideal solution. But you can also check the current grounds for the lights to make sure they are making a solid connection to a clean metal surface.

What you described is the classic insufficient ground scenario so finding a way to improve the grounds will fix the problem.

expert reply by: Jameson C