Trailer Brake Controller Works with Manual Override but Not with Brake Pedal

Updated 07/29/2014 | Published 07/27/2014

Question:

The lever on my controller will work the brakes but the truck pedal wont. Does the battery need to be installed in the trailer so the breakaway switch works? Would that cause the truck brakes not to work the trailer brakes?

asked by: Carroll S

Expert Reply:

Since the controller is activating the trailer brakes when you use the manual override that means that the trailer battery not being connected is not the problem. Both the brake pedal and the manual override will tell the controller to send back power on the same wire so that battery is not the problem. Although you should have it connected for safety.

When a controller works with the manual override but not the brake pedal that indicates a problem on the red wire. The red wire is the input wire telling the controller that you are stepping on the brakes. If the connection from the red wire to the truck looks fine (you could always try re-establishing the connection) then the issue could be a blown stop light or CHMSL fuse. Use the truck owners manual to find the fuse locations.

There are some tests you can do to test the controller. In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # PTW2993 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override or brake pedal. If it shows power at idle, then there is something wrong with the controller and it will need to be replaced. Please note that some controllers require that the trailer and vehicle be moving to work with the brake pedal.

I have included some links to the right that explain how to test and troubleshoot a controller.

expert reply by: Michael H