Troubleshooting Trailer Brakes That Remain Engaged When Trailer Is Connected To Vehicle

Updated 05/15/2015 | Published 05/14/2015

Question:

When I plug in my 7 way harness, my trailer brakes are engaged and do not unengage. The only way I can disengage them is to unplug the 2 pin plug from the underside of the truck harness. Thus creating my trailer brakes useless. Except for the break away system. How do I fix this problem?

asked by: Scott H

Expert Reply:

The first thing to check is the connectors to make sure there is no corrosion present. That can cause a variety of problems. If that checks out you will need to do some other testing.

You can sever the blue wire about 4 to 6 inches from the back of the brake controller and see if the problem still exists. If it does, then you have something wired incorrectly, or the brake controller needs to be replaced. I have attached a drawing that shows how the wiring should be run for a brake controller.

If that checks out okay, you will need to move to the trailer side and check the wiring for the breaks and the breakaway switch. If the pin is loose for the breakaway and not engaged properly, that can cause the problem as well. I have attached a helpful article that explains installation of a breakaway system on a trailer.

I have also attached a helpful article that explains how to test the trailer brake magnets you can check out.

expert reply by: Jeffrey L