Troubleshooting Trailer Brakes that Randomly Lock Up on Trailer

Published 04/30/2025

Question:

have a car hauler 20 foot trailer that no matter what we hook to the brakes will randomly lock up an you tell me what issue i have,Thanks Mike

asked by: Mike M

Helpful Expert Reply:

Hey Mike, that would indicate you have a short between the brake output circuit and the 12 volt accessory circuit that is intermittently making a connection that is locking up the trailer brakes. You'd need to go over the two circuits looking for any cut or exposed wire and fix as needed. How often are they locking up and for how long though?

expert reply by: Jameson C

Mike

4/30/2025

Pretty often sometimes I have to unplug to get to release

Jameson C.

4/30/2025

@Mike Does it seem to happen if you hit a bump? If you shook the trailer wiring harness would that make it lock up or unlock? You should be able to hear the assemblies click and hum if you were parked and standing near them.

Mike

4/30/2025

@JamesonC I will try that Thank you are you saying from trailer plug to 12 volt supply

Jameson C.

4/30/2025

@Mike Shake the wire harness that plugs into your vehicle 7-way. Basically try and simulate hitting a bump to see if you can get it to lock up and go from there.