Wiring Codes AUX and CHMSL During Brake Controller Install on 2003 Chevrolet Trailblazer

Published 02/23/2011

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Question:

I purchased a brake controller. On my 2003 trailblazer the wiring codes are called AUX and Chmsl. What do they stand for. The other two wires I can cross reference but I can not figure out these two codes to finish wiring. Thanks

asked by: Dan P

Expert Reply:

The code AUX refers to auxiliary, which is auxiliary power, which should be the Dark Blue wire on your 2003 Chevrolet Trailblazer. This wire will connect to the Dark Blue wire on the brake controller and should be connected to the 7-way as the brake output wire.

The code CHMSL refers to Center High Mounted Stop Light, which is your third brake light circuit. This is the brake signal wire and will be connected to the red wire on the brake controller. This wire should only get signal when the brakes are applied. You can double check this by testing the wire with circuit tester, part # PTW2993.

I made an illustration showing the vehicle wire colors that need to be connected to the brake controller wires. You will want to double check this with a circuit tester, part # PTW2993 as vehicle manufacturers change vehicle wiring colors often.

I have linked a video installation of a brake controller on a 2006 Chevrolet Trailblazer that you may find as a good reference. I have also linked an FAQ Article on brake controllers.

expert reply by: Reno H