Obtaining Brake Stoplight Switch Signal for Brake Controller Install On 2011 GMC Terrain

Question:

Have most of the wiring connections completed, but ran into a snag with the controller brake switch. Seems this vehicle has a sort of variable low voltage potentiometer that runs directly to the body control module, not the usual brake light switch. Where do you pick up the brake signal for the controller? Manual says that ABS will not function if supply is taken from BCM wiring. Also, we installed a continuous duty relay, to isolate, the trailer charge wire. Will the induction voltage from the coil in this relay be sufficient to harm the BCM when the relay is turned off? Like an answer soon, as we need to complete this task.

asked by: Roger M

Expert Reply:

The brake stoplight signal can be accessed at the BCM, as you are sitting in the driver's seat, the BCM (Body Control Module) is located under the dash above where your left knee would be. The module (think of it as a junction box) will have 7 different wire connectors that plug into it. Look for the black connector (all the connectors are different colors) that has 26 different slots for wires to insert into. In wire position # 11, there will be a white wire that carries the brake stoplight signal. Use the quick connector to tap the red brake controller wire into this circuit, and you will be good to go. Be sure to use a circuit tester like part # PTW2993 to confirm that the white wire only shows voltage when the brake pedal is pressed.

I have edited a diagram showing the location of the BCM, as well as the # 11 wire position in the black connector.

expert reply by: Mike L