Horse Trailer Brakes Lock Up When Using a 4-Way Flat Trailer Connector for Trailer Lights

Question:

I have horse trailer with brakes that lock up when standard 4-flat is plugged into jeep every time brakes are hit, and occasionally intermittenly locking while driving. This trailer is equipped with a brake controller and an entire different plug to use, but my jeep does not have the required plug to even use the controller, and the batteries in the controller are completely dead. This thing hasnt been used in years. So we only hook up the standard 4-flat to run lights, and somehow with the 4-flat plugged in, it activates the trailer brakes. I didnt even think the 4-flat would be connected to trailer brakes at all. I just pulled this trailer 2000 miles with none of this non-sense happening. It just started the last time I was hitched up. When I unplugged the 4-Flat, all brake problems go away. I Dont having a wiring diagram, but dont understand how 4-flat wiring meant for lights can somehow short over to a brake system that is unplugged and just along for the ride.

asked by: Chris

Expert Reply:

You are correct that the wires from a 4-way flat trailer connector should have nothing to do with a trailer's brakes or a brake controller, and it is hard to say what is causing the trailer's brakes to activate. It is possible that somehow the wires for the turn and brake signal are touching the brake wires, causing the brakes to activate when the turn or brake signal is activated.

You can try checking all of the trailer wires for damage, such as pinches or tears, where the wires could be touching. You may find a solution in repairing damaged trailer wires.

Likely, the best solution will be to re-wire the trailer. This will help solve any hidden problems with the existing wiring. The Deka Bonded 4 Wire # 16-4B-1 is sold by the foot and will provide you with the wires needed to connect tail, turn, and brake signal lights, as well as a ground wire. A trailer-end connector, like the Hopkins Endurance 4-Way Flat Trailer Connector # HM48110, will work to connect your trailer's wiring to your Jeep.

To re-wire your trailer, you will also want some additional parts, like the Deka Heat Shrink Butt Connector 12-10 Gauge # DW05745-10 to connect the wires, Deka Ring Terminal # DW05740-1, and a self tapping screw # FA1131822 to ground the wiring to the trailer's frame.

I have attached a help article on trailer wiring diagrams for you to help in re-wiring your trailer.