Troubleshooting Trailer Brake Controller That Outputs 4 Volts with No Brake and No Manual Override

Updated 05/31/2016 | Published 05/27/2016

Question:

Hi, I get just over 4 volt when the breaks or the override are NOT applied. Only if I unplug the break controller does it go to 0 volt. Is the controller bad? Thanks.

asked by: Norbert

Expert Reply:

If you are testing at your vehicle's 7-way and are detecting just over 4 volts on the brake circuit when neither the brake pedal nor manual override are engaged then you may have a bad controller, or you could have a short in your trailer socket that is allowing the 12V power circuit to bleed over to the brake circuit. Carefully inspect the 7-way (inside and out) for signs of corrosive build-up that could be bridging circuits.

If you are testing the controller's output on the blue wire right at the back of the controller (before it enters the vehicle wiring) and you detect 4 volts there with no brake pedal and no override, then the unit is either mis-wired or is damaged and should be replaced with a controller like the Prodigy P2 # 90885. The red wire to the controller must be connected to the cold side of the brake light switch, which carries power ONLY when the pedal is pressed. Any other wire could be delivering 12V power that could fool the controller into thinking you're pressing the brake.

Depending on your vehicle, you may be able to use a quick-install wiring adapter to install this reliable and highly-rated proportional controller. Several articles are linked for you to help with your troubleshooting effort and selection of a new controller if one is needed.

expert reply by: Adam R