Trailer Brakes Activate as Soon as Truck Starts to Move

Question:

trailer brakes come on as soon as the truck starts to move,also the right brake/signal light does not work. This is behind 99 F-250 which works fine on camper at home.Also trailer works fine on other trucks.

asked by: Ernie

Expert Reply:

Starting with the brake issue, does your trailer use a 6-way connector and are you using a 7 to 6-way adapter to connect to the 7-way connector on your F250? If so, this is a common occurrence. There are two generally accepted ways of wiring a 6-way connector. One uses the center pin as the 12-volt accessory power feed to the trailer, the other uses the center pin as the brake voltage output circuit. If your adapter is wired one way and the trailer the other, the brakes will be getting a constant 12-volts and will lock. We offer a universal 7 to 6-way Adapter, part # 47549 that can be wired either way.

To troubleshoot the lamp issue, you first need to determine if the problem is in the vehicle or the trailer wiring. Use a circuit tester like part # 40376 to test the pin for the right directional/brake light on the trailer connector. If you do not get a signal on this pin as the turn signal is activated, the problem exists on the vehicle. You will have to trace the wiring for the trailer connector and look for a loose connection. If you do show power on this pin, the problem exists on the trailer. Make sure that the trailer connector itself is in good condition with no damage or corrosion. Trace the wire that carries the right directional/brake light circuit back to the lamp, looking for pinched or broken wires or for cracked or worn insulation on the wire that would allow the copper conductor to contact the trailer frame.

expert reply by: Mike L