Where To Connect the Red Brake Wire From the Electric Brake Controller on a GMC 3500

Updated 09/06/2011 | Published 09/03/2011

Question:

I dont know where to splice the cold side of the brake light indicator wire the red wire on the brake controller going to the tow vehicle. Is it the tail lite?? Pls help, cant afford to have this professionallly done. I think there should be a wire coming off master cylinder. Pls help. Thx. Electric Brake controller - GMC 3500

asked by: Carl O

Expert Reply:

When installing a brake controller like the Tekonsha Prodigy P2 brake Conroller, part # 90885 in a tow vehicle the red wire is the brake switch wire that is connected to the cold side of the brake switch on the tow vehicle.

To determine which wire to use on your GMC 3500 for the stoplight circuit from your brake controller you should use a circuit tester like the, part # 3808, to test the wires on the brake switch that is located above the brake pedal. You will need to test the wire that has voltage when the brake is applied and then no voltage when the brake is not being applied. Once you find that wire, you have found the wire you should connect to the red brake circuit wire of your brake controller.

I am including a link to a FAQ page on Brake controllers and a link to the installation instructions on the Prodigy brake controller.

expert reply by: Jeff D