Troubleshooting Brake Controller that Applies Brakes When Vehicle Engine Starts

Published 12/13/2017

Question:

When connected with engine off the screen reads .c as it should. When engine is started controller applies brakes and reads whatever the knob is, adjusted to. You can only release brakes by adjusting controller to minimum. Is it bad?

asked by: Mike C

Expert Reply:

It sounds like your brake controller is not installed correctly or has a short because you have the 12V constant on your brake controller when engine is running. This could be a wiring harness issue if you have a custom harness, a 7-way connection issue if there is corrosion in the connector, or you may have the red wire from your brake controller connected to the hot side of the brake light switch versus the cold side.

If you hardwired your trailer brake controller, I recommend checking the brake light switch connection first. You can use the circuit tester # PTW2993 to check this connection as that red wire should not have signal when the brake pedal is not pressed. You can check this with the custom wiring harness as well.

If that isn't the issue, I recommend cleaning your 7-way on both your vehicle and your trailer side to make sure there isn't any corrosion causing a jump connection to your electric brake output.

If that isn't the issue, then your brake controller may be malfunctioning and need replaced.

I've attached a few articles to assist in your troubleshooting as well.

expert reply by: Jason S