Trailer Brake Lights Kick Off While Running Lights Are On

Published 10/16/2019

Question:

When I hook a trailer to my truck if I turn the running lights on and apply the brake the left side on the trailer does not work if I let off the brake I have a running light if I turn the lights off on the truck and apply the brake the brake light turns on like they are supposed to

asked by: Ed

Expert Reply:

The issue you are experiencing with the running lights causing the brake lights to cut out is caused by a poor ground as with most trailer lighting issues. That said, when most people check the ground they simply look at the wire and make sure it is still attached but this is not sufficient. I am not sure how your trailer tail lights are grounded but you will need to remove each one, make note of the ground used, and then re-secure with a new bare metal surface ground. This will need to be done for each tail light and the main trailer ground. If you still have issues then I recommend running a jumper wire from each tail light to the main trailer ground. If you don't already have a junction box such as the Pollak 7-Circuit-Breaker Junction Box part # PK52249 this will make troubleshooting much easier in the future.

I have attached a trailer wiring help article you will want to look through as well below.

expert reply by: Conner L