GM Service Manual Online
For 1990-2009 cars only

When the ignition is in RUN, pass through voltage is available to the switch side of the heated mirror relay from the MIRRORS fuse in the underhood fuse block through CKT 1040 (ORN). When the rear window defogger switch is pressed, the solid state time delay relay actuates the heated mirror relay feed voltage through CKT 293 (PPL), to the coil side of the heated mirror relay. With ground being provided through CKT 150  (BLK) to G202, the relay is energized allowing the pass through voltage to be applied to the heated mirrors. CKT 267 (ORN) provides the connection between the heated mirror relay and the mirrors. Ground is provided for the heated mirrors through CKT 150 (BLK) to G202. Depressing the rear defogger switch will energize the heated mirrors and the rear defogger(s).