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Finding the Third Brake Light Wire on a 2013 GMC Sierra 2500HD for a Camper Shell


I am trying to locate the exact location of the wire provided to add a third brake light to a 2013 gmc sierra 2500 hd


Expert Reply:

There may be a wire loom under the truck, above the spare tire with some tow package wires in it. If you cut back the loom, often times there will be 2 additional wires. The Light Blue wire provides a lead for a camper shell brake light. The other, a Light Green wire, is for the reverse lights.

To make sure you have found the correct wires, use a circuit tester like # PTW2993 to test the wires.

If this wiring is not present, to add a third bake lamp you would need to tap into the turn signal circuits to get the brake light signal. Because the brake lamp and turn signals are combined into the same circuit, you would need a vehicle-to-vehicle tail light converter like part # 118158 to split out the brake lamp circuit, otherwise your 3rd stoplight would blink with the turn signals.

The converter has 3 inputs, a right turn, left turn and a ground. The easiest place to access the wiring would be the harness behind the taillight assemblies. Tap the green wire into the right turn, the yellow wire into the left and ground the white wire to the truck frame. (My testing indicated that only one of the wires need to be used but using both would make for a more reliable connection.) The red wire exiting the output side of the converter would provide your brake light signal, independent of the turn signals. The green and yellow wires on the output side could be capped off.

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