Hooking Up Wiring for a Third Brake Light on a Camper Shell for a 2008 GMC Sierra

Question:

Just need some basic instruction on to wire the canopy brake light to the truck?

Expert Reply:

You have a couple of places you can look for the center high mount stop light (CHMSL) circuit on your 2008 GMC Sierra. First, you can check beneath the truck where the trailer wiring runs underneath. You can test the wiring there with a circuit tester like # 3808 if needed, to determine if any of the wires in the loom are dedicated brake light wires.

If you have a wire bundle or trailer wiring leading to a trailer connector located above the spare tire, look for a light blue wire and test it for function to determine if it is the correct wire.

The wire could also be along the driver side frame rail near the back of the truck specifically for a camper shell brake light.

Finally, under the dash and below the steering column there is a tow package wiring bundle that is held together with a white tag. In this wire bundle there should several wires and the functions of each will be on the tag. Test the wires and find the one that only shows a signal when the brake pedal is pressed but not when the turn signals are on.

expert reply by:
Michael H

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