A camper shell or truck cap third brake light (the center high-mount stop light, or CHMSL) connects to the same circuit that feeds your truck's own third brake light. You tap one wire for power and run one to ground.
Pick your truck
We've documented where the CHMSL wire is on popular trucks:
Wire colors on our light
| Wire | Connects to |
|---|---|
| Red (+) | The truck's CHMSL / third brake light power wire |
| Clear (−) | Ground: bare metal on the truck frame |
Steps
- Find the CHMSL wire using the guide for your truck above.
- Confirm it with a test light. Clip the test light to ground and probe the wire. It should light only while someone presses the brake pedal, and not with the headlights or turn signals.
- Route the lead. Our light includes 7 feet of wire. Run it from the shell to the tap point along existing harnesses and away from the exhaust and moving parts. If the source wire is farther than 7 feet, extend it with wire of the same gauge.
- Add a disconnect at the shell. A two-pin weatherproof plug lets you remove the shell without cutting wires.
- Make the connections. Solder and heat-shrink, or use sealed crimp connectors. Connect red to the CHMSL wire and clear to a clean, bare spot on the frame.
- Test with a helper on the brake pedal before closing up panels.
On some trucks the ground must go to the metal frame rather than the body. When in doubt, use the frame.
Common questions
What is a CHMSL?
Center high-mount stop light: the official name for a vehicle's third brake light.
My truck's wire isn't where the guide says. What now?
Harness colors and routing change between trims and model years. Use a test light to find the wire that is live only when the brake pedal is pressed, or contact us with your year, make and model.