Installed New Electric Brakes and When I Plug the Trailer Into the Truck they Lock Up

Question:

I just installed new electric brakes on my daughters 2 horse horse trailer. When I plug the trailer to the truck I have lights and turn signals. When you step on the brake, the elec brakes automatically lock up and will not release. The controller inside the truck only has a dotinch no number reading. The breakaway battery is dead. I have the trailer hooked up to my 1995 Dodge Ram 1500 pickup. I had to replace the brakes and tires because the electric brakes locked up on the trailer when she was pulling it with our 2000 Ford F350 dually. The trailer hook-up uses an adapter. Any idea what the problem may be?

asked by: Greg

Expert Reply:

It sounds like you have a wiring issue between the truck, adapter and trailer connector.

I would start at the factory 7-Way on both of your trucks and test them for proper function. The photo I added shows the proper function for each terminal inside the 7-Way connector. Once you are sure the vehicle side connectors are wired correctly you can turn your attention to the trailer and make sure the connector on the trailer, I am assuming a 6-Way since it is a horse trailer, is wired correctly, see photo. You will need to keep in mind that the 6-Way connector has two acceptable wiring configurations. One where the power wire is in the center and the brake output wire is in the 2 o-clock position and the other has the brake output wire is in the center and the power wire in the 2 o-clock position. This could be the issue you are running into.

If you find that you have power to the trailer brakes anytime you have the trailer connected to the trucks with an adapter like part # HM47570, you will either need to rewire the trailer end connector to the correct configuration for use with the adapter, or you will need to rewire the inside of the adapter to match the wiring on the trailer.

expert reply by: Robert G