Hello, I made a headache rack for my truck that has the third brake light on it, where in the cab and what wire goes up to the third brake light on my cab? I want to splice that wire and run it to the third brake light on the rack. Thanks! Kyle

 

Hand's down easiest way to wire a rack is to use the 4 or 7-pin on the back of the truck. No cutting, no splicing, it's all clean. It would be easier to splice into either the trailer harness or a rear brake light to get the light working instead of fishing around in the cab for the 3rd brake light wire.

Mine runs off the 7-way, has backup lights, brakes lights, turn signals, and driving lights.

 

just pull out the light and tap the brake wire there, then run it to your racks lights, seems the most simple way

 

If it's a 3rd brake light, then you will need to tap into the wire going to the 3rd brake light on the cab. If you tap into the trailer wiring, it will flash with one of the turn signals.

The technical name for the 3rd brake light is Center High Mount Stop Lamp. (CHMSL) Federal Motor Vehicle Safety Standards require that the CHMSL illuminate ONLY when the brakes are applied.

 

kd0axs is exactly right. I added a third brake light on my truck cap and I tapped into the CHMSL wire. On mine, it was under the truck in the wiring harness near the spare tire. The wire was just blunt cut with a piece of heat shrink on the end and it was labeled "CHMSL"

Hope this helps.

 

Now that you mention it, I think I remember seeing that wire under my truck too.

I'd go out and take a look, but I don't really feel like laying in the snow right now.