Trailer Towed By 2004 GMC Sierra Applies Brakes Instantly When Trailer is Plugged In To Vehicle

Question:

recently got a 2004 GMC sierra 2500. It has a voyager brake controller. Tried to tow a trailer with brakes and the brakes would not release, tested the plug and its getting a constant 12v feed, unless I unhook the controller, tried a different controller and still having the same problem.Any information will help.

asked by: Anthony

Expert Reply:

Are you by chance using a 7-way to 6-way adapter on the vehicle? There are two generally accepted methods of wiring the 6-way connector. One uses the center pin as the 12-volt accessory power feed, the other uses the center pin for the brake output voltage. If the adapter is wired one way and the trailer is wired the other way, the brakes are going to get 12-volts immediately upon plugging the trailer in.

If you are not using the adapter, your trailer connector is most likely wired incorrectly. Try using a circuit tester like part # PTW2993 and testing each pin on the trailer connector for function. If the pins on the connector are compared to the hands of the clock, the pin at the 1:00 position is the 12-volt accessory feed. This pin should show constant voltage. The pin in the 3:00 position should show voltage when the right turn signal and brake is activated. The pin in the 5:00 position carries the brake controller output voltage and should go hot when the manual brake switch is used on the brake controller. The 7:00 pin is the ground, 9:00 is left turn/brake and the 11:00 is the running lights. If you determine that the vehicle trailer connector is wired incorrectly, examine the connector on the trailer itself and verify that it is correctly wired. You can use a car battery to power up each pin on the connector if needed to verify function.

I will link you to our Wiring FAQ article that features wiring diagrams and other helpful information about trailer wiring.

expert reply by: Mike L