Circuit/System Description
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The brake switch indicates brake pedal status to the control solenoid (w/body and TCM) valve assembly. The normally-open brake switch supplies ignition voltage to the TCM. Applying the brake pedal closes the switch, suplying voltage to the TCM. Releasing the brake pedal interrupts voltage to the TCM.