Trailer Running Lights Only Work While Coupled To Trailer

Updated 10/14/2019 | Published 10/13/2019

Question:

I have a vintage travel trailer with grounding issues. The only time I can get the running and rear lights to work Is with the ball in the coupler. I have a ground wire that connects the trailer harness to the truck and I have checked the truck grounding wire. I have a couple truck that all pull utility trailers on a daily basis and none have issues. I have tried lots of troubleshooting but nothing’s has worked. The trailer harness is also new.

asked by: Zac M

Expert Reply:

The issue with your running lights is indeed caused by the trailer and the lack of a solid ground. That said, this is an easy fix as all you will need to do is run a ground jumper wire from each running light to the main trailer connector ground and then re-ground all of these wires to a new bare metal surface on the trailer coupler that is free of paint. If the ring terminal crimp is not tight or the crimp for the running light ground wires is also not tight then this will affect continuity so be sure to check this as well.

I have attached a trailer wiring help article for you to look over.

expert reply by: Conner L