The rear window defogger system consists of the following components:

When the rear defogger switch pressed, a signal is sent from the HVAC control assembly to the instrument panel cluster, the instrument panel cluster then sends a serial data message to the rear fuse block. The rear fuse block interprets as a request for the rear window defogger system. The rear fuse block enables the rear window defogger system by supplying ground to the REAR DEFROST relay coil. With the relay energized, battery positive voltage is allowed from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. Ground for the rear window defogger grid is provided by G403.