Troubleshooting Brake Controller That's Actuating Brakes When Unplugged

Question:

I have a 2005 e 450 I installed the brake control and the trailer locks up when I hit the brakes and I tried to turn the dial down and it doesnt help so I unhooked the control on the back side but left the harness hooked up to the factory plug and I still have trailer brakes. When hooked up the controller it show no trailer also.

asked by: Jay

Expert Reply:

You're saying that you still have trailer brakes even though the controller's been unplugged? If that's the case, then there is a short in the trailer connector on the vehicle or on the trailer that's allowing power to bleed over from a different circuit to provide power to the trailer brakes. If the short isn't located in the connectors, it's likely on the trailer.

Closely examine the connector on the vehicle and on the trailer. If you see any green or white corrosion on either connector, the corrosion might have spread to the interior of the connector and could be allowing power to bleed to the brake output circuit. Clean or replace trailer connector as needed. Trace the brake output circuit, making sure there's no cracked insulation or pinched wires that would allow a short circuit.

I've linked you to our Brake Controller Troubleshooting FAQ.

expert reply by: Mike L