Electric Trailer Brakes Just Started to Lock Up when the Trailer is Connected to Tow Vehicle

Question:

I have a utility trailer with electric brakes. The previous owner had a 5-point plug and I replaced it with a 7-point to match my truck. For some reason, he had the electric brakes disabled. The blue brake wires are all cut, and there is no blue wire running to the 7-point plug. The white ground running to the back is cut near the wheels. Everything worked fine. The last time I tried to use the trailer, the brakes locked up. If I unplug it, rolls fine. Could it be the breakaway brake system? If the battery is dead, would that make the wheel brakes lock up? This is a small utility trailer. I dont need brakes, and they appear to be disabled per cut wiring. Is there something in the wheel and brake that would lock up? Thanks.

asked by: Butch G

Expert Reply:

Since the brakes are locking up when the trailer is connected and release when the trailer is not connected then the brake magnets have to be wired to something. My guess is that the 5-Pole was not original on the trailer and the previous owner used some alternate wiring for everything.

First we need to get the wiring right as far as which wires does which function. I have included a link to our help article on trailer wiring with diagrams that show the functions of vehicle and trailer side connectors. Ignore the colors because any color could have been used. The key is to look at the functions and where they are in the 7-Ways.

It could be that there is a problem with the breakaway system wiring so you can inspect its wiring and repair as needed. Make sure the ground is attached to a corrosion free bare metal surface. The breakaway system can only send power to the brakes if the pin is pulled out of the switch completing the circuit. To determine if it is the breakaway system you can disconnect it and if the brakes do not lock up then that was at least part of the problem.

There could also be a short caused by dirty or corroded trailer connectors. Make sure the vehicle and trailer side connectors are clean and free of corrosion inside where the wires attach and outside on the pins.

expert reply by: Michael H