Troubleshooting Trailer Brakes that Lock Up When Headlights Are On

Published 10/17/2023

Question:

When I turn on the head lights the trailer brakes apply - is it the controller or a trailer problem.

asked by: Brian

Expert Reply:

You have a short between the running light circuit and the brake output circuit of your trailer wiring. So what you will need to do is go over the wiring behind both connectors (trailer side and vehicle side) looking for any obvious shorts like exposed wire and fix as needed. It's almost always near the connectors but it could also be on the wiring further up from the connectors so you would want to check there as well.

expert reply by: Jameson C