Wiring a Third Brake Light and Cargo Light on a 1989 GMC K2500 Series Pick Up Truck

Question:

Presently no cargo lamp. Headed to the paint shop next week. I was going to have the paint shop install the light, but where do I find power/brake light wire. The cargo lamp should just wire into the interior dome light?

asked by: Jon H

Expert Reply:

You will need to find what is called the CHMSL circuit (center high mount stop light) to wire a third brake light on your 1989 GMC K2500. You could use the vehicle owners manual of the legend on the power distribution box lid to find the fuse location and use a fuse tap to power the third brake light.

There may be a wire under the truck for this function. Places that install truck bed camper shells may know where it is located. You would not use trailer connector wiring because the brake lights are combined with the turn signals. Check above the spare tire for a wiring harness that will have a wire loom around it. If the harness is there, look for a light blue wire, which carries the CHMSL circuit. You need to wire a switched 12v circuit for a dome light or tap in a switched circuit to the running lights.

For the interior light you could wire it into the same circuit as the dome light. That way you would not have to install a separate switch for the cargo light.

expert reply by: Michael H