Trailer Brakes Only Work When Manual Switch on Brake Controller is Activated

Updated 11/16/2010 | Published 11/15/2010

Question:

Hi, i am having trouble with my trailer brakes, i have already replace the magnets and the drum hubs, and my trailer will only brake with the trailer brake control by hand not when i press my truck brake pedal. Thank you

asked by: Jose G

Expert Reply:

The controller is only putting out voltage when the manual switch is applied on the brake controller, but not when the vehicle brakes are applied, is that correct?

The most likely problem is that the controller is not getting the input that the vehicle brakes are being applied. When the trailer is hitched up with the transmission in park, use a circuit tester like part # 3808 on the red wire exiting the rear of the controller. You should show voltage on the wire when the trucks brake pedal is pressed. If you do not find any power on this wire, you will need to trace it back to its connection to the brake stoplight switch located at the top of the brake pedal. Make sure that this connection has not come loose, and that it has been connected to the correct circuit. The circuit that the red wire is tapped into should also show voltage only when the brake pedal is pressed.

Please get back with me and let me know what you find.

expert reply by: Mike L