Troubleshooting Trailer Taillights that Stop Working When Brakes or Running Lights Come On

Question:

I figured it out. I had a four prong that I converted to seven and it had a secondary ground that I taped up because I didn't see it as necessary but it was the culprit. Thanks Jameson

asked by: Michael W

Expert Reply:

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

Michael W.

8/21/2018

I figured it out. I had a four prong that I converted to seven and it had a secondary ground that I taped up because I didn't see it as necessary but it was the culprit. Thanks Jameson