GM Service Manual Online
For 1990-2009 cars only

The brake indicator in the instrument cluster alerts the operator of problems in the vehicle's braking system. With the ignition in the RUN, BULB TEST or the START position, voltage flows to the instrument cluster through CKT 39 (PNK) form GAUGES fuse 4. The BRAKE indicator lamp is illuminated whenever CKT 33 (TAN/WHT) from the instrument cluster is grounded.

The brake warning indicator illuminates if the parking brake is applied while the ignition switch is in the RUN or the START position . This alerts the operator to release the parking brake. The parking brake warning switch is mechanically grounded. The switch contacts close when the parking brake is applied grounding CKT 33 (TAN/WHT). The brake pressure differential switch closes the contacts when conditions in the hydraulic brake system are abnormal. This grounds CKT 33 (TAN/WHT) and CKT 680 (PPL) through CKT 150 (BLK) to G105.

The electronic brake control module also grounds CKT 33 (TAN/WHT) if there are abnormal conditions in the antilock brake system (ABS). The brake indicator lamp and the antilock brakes warning indicator lamp both light for ABS failures.