For 1990-2009 cars

Fuse #20 supplies B+ to the driver and passenger seat heater relays at all times. Fuse #4 supplies B+ to the left and right rear seat cushion heater relays at all times. When the ignition switch is in the ON position, fuse #15 supplies B+ to all of the heater relays. The driver seat and passenger seat heater relays are permanently grounded to G103. The left and right rear seat cushion heater relays are permanently grounded to G200.

The heated seat thermal switch maintains the heated seat element temperature between 40°C (104°F) and 50°C (122°F). The thermal switch regulates the seat's heating element temperature, and NOT the actual seat cushion temperature. Each seat contains two heating mats and a built-in thermal switch for each mat. The heating mats are cemented to each seat cushion and each seat back cushion

When you press any of the heater switches, B+ is input into terminal 5 of the corresponding heater relay. The heater relay responds to this input by closing the switch and supplying B+ to the appropriate seat cushion heater. The heated seat element will energize and the built-in thermal switch maintains it's temperature between 40°C (104°F) and 50°C (122°F). The seat cushion continues to warm until you press the corresponding heater switch again, or until the ignition switch is turned to the OFF position.