2018 Chevy Colorado ZR2 CHMSL Third Brake Light Wiring

If you got a GFC and want to wire up the 3rd brake light here are some tips.

  • The turn signal and brake light signals are combined on the tail light assembly in the new gen Chevy Colorado. This means if you tap that signal for the GFC 3rd brake light (CHMSL Center High Mounted Stop Lamp) from the tail light module your stop lamp will flash with the turn signal that you tapped into. This is generally uncool and also could get you pulled over and ticketed in some states.

  • If you still want to use the rear turn signal/taillight module for the signal source of the GFC’s CHMSL you can, but you need to add a logic module to separate out the brake signal from the turn signal. Annoyingly, this approach requires that you wire the logic module into both tail light modules which is a fair amount of wiring and requires an additional component.

  • The other approach, and the one that I used, was to find the signal from the CHMSL in the Chevy wiring harness and tap it. Chevy did not run this to the back of the vehicle so the best place that I found to tap it was under the UHC (Underhood Electrical Center). Basically, you need to remove the fuse box and tap the right wire and then run a new wire to the back of the truck. I am not going to describe this process in detail but you find all about it on the internet and I would just say to take your time and be careful. Although the fuse box to Connector interface if pretty cleverly designed by GM you can really create some big electrical issues here if you are not careful so take some time to figure it and be cautious if you haven’t done it before.

To find the CHMSL signal wire I searched the interwebs and found a GM procedure to install the ZR2 Sport Bar which involves a new CHMSL on the sport bar. This forum would not let me attach that file (PDF) but if you search for ZR2 GM Sports Bar Install you can probably find it. The wire for the CHMSL is described as : “VT/GY in cavity 75 of connector X”. Please see my pictures attached.

Once the wire is tapped, it is a matter of running the wire back to the rear of the truck and into the bed. I entered the bed through the grommet in the back and put the connector there from GFC just inside.

Using this approach the GFC’s CHMSL and the truck’s factory CHMSL both light up in parallel when the brakes are applied. If the GFC is ever removed, just unplug the GFC connector and the truck’s CHMSL still works as always.

IMHO this is the cleanest and best approach. I hope that this helps anyone with a Chevy and a GFC to find the signal to connect that 3rd brake light and not have the brake light flashing when they turn.

Happy Trails.


I was able to tap into the BCM on the driverside floor board

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I was hesitant to take the fuse box apart so I went in search of the same wire in the cab. I located the wire leading to the CHMSL in the cab and spliced into it there. Its under the kick panel trim on the left side doors. Pics are of the left rear door on a crew cab. The wire is purple with a grey line on it. It was right on top of the bundle of wires in my truck. Tested it by sticking a sharp test light probe through the plastic and found it on the first try. Ran the new lead through a plug in the floor under the seat and then along the frame to the camper wires.



Appreciate all this detailed info… I can already tell this will be a bit over my head. Anyone have thoughts as to if this is worth it? I’m not sure if I want to go through the hassle to try myself, pay someone, or just have it blink with my blinker. Also thinking I may just go without the 3rd brake light altogether…

In some states the third brake light is required…check your local laws.

Yes, it is worth doing and if it’s worth doing, it is worth doing right.