Chevy / GMC 3rd brake light wiring

Where to connect a camper shell third brake light on Chevy / GMC trucks. Red (+) to the CHMSL wire, clear (−) to ground.

Find the CHMSL wire on any truck

We're still documenting Chevy and GMC locations by year. This method works on any truck:

Start at the truck's own third brake light on the cab roof, or at the driver's side tail light harness.
Clip a test light to ground and have a helper press the brake pedal.
Probe the wires until you find one that lights only with the brake pedal pressed (not with the headlights or turn signals). That's the CHMSL wire.
Connect the red (+) lead to it and the clear (−) lead to bare metal on the frame.

Tell us your year and model on the contact page and we'll point you to the wire.

Wire colors and locations can vary by trim and model year. Always confirm with a test light before connecting.

Need the light?

LED 3rd brake light for A.R.E., Leer, ATC, Astro, Jason and Century caps.