I am not getting a signal to my new P3 brake controller. Where can I find the cold brake wire on a 2005 GMC Sierra. I think the box that the harness plugs into may be missing a connection so I want to wire it directly to the controller.
Expert Reply:
The first thing I would do is check all your fuses. I believe that circuit is shared with the third brake light. The cold side wire is located under the dash in the large wiring harness by the steering column. It is typically a white wire (although color varies from year to year). The wire can be difficult to locate. You will need to use a circuit tester, like part # 40376, and probe wires until you find one that only shows current when the brake pedal is pressed.
The wire should be light blue, but this can vary even within the same truck in the same model year. Always check with a circuit tester to be sure.
expert reply by: Mike
