Troubleshooting Trailer Brakes That Apply When Trailer Is Placed In Reverse

Question:

I have a 2003 Tundra with tow package installed when purchased. I tow a 1979 Air Stream. I use a P3 controller, When I put the truck in reverse the trailer bakes lock up and a 10 amp gauge fuse blows in the truck. Im not sure where to start. I have been unplugging the trailer every time I back up

asked by: Pat

Expert Reply:

I'd be curious to know which fuse is blowing and if this is a suddenly occurring problem or if it has been happening since the first time you used the trailer with that truck.

If the trailer brakes are being applied when the vehicle is placed in reverse, two possibilities immediately come to mind:

1) Either the connector on the trailer or on the vehicle is mis-wired. Since the Tundra has the factory tow package, I'd suspect that the mis-wire is on the Airstream, unless the connector on the Tundra has been messed with. I'll link you to our trailer wiring FAQ article that shows how the connectors should be wired.

2) There's damage or corrosion in the connector on the trailer or the vehicle that's allowing the signal to bleed from the reverse lamp circuit to the brake output circuit. Check the connector on the vehicle and on the trailer, looking for damage or green/white corrosion. If the corrosion is severe enough, it might have traveled to the interior of the connector where the wires attach to the terminals and created the short.

expert reply by: Mike L