The rear heater switch controls the rear heater. The following components provide battery voltage to the rear heater and air conditioning (A/C) relay (rear):

The coil of the relay is grounded by CKT 850 (BLK). The coil of the relay energizes when the ignition switch is in the RUN position. The energized relay provides battery voltage to the rear heater switch. Fuse M2  (RR HEAT/A/C) provides battery voltage to CKT 742 (RED) and the common contact of the A/C relay (rear). The common contact and the normally open contact connect when the relay energizes. The connected contacts provide power to CKT 1923 (ORN). The energized CKT 1923 (ORN) supplies the rear heater switch.