Circuit/System Description
WARNING: This page is about a different car, the 2010 Cadillac SRX. However, it is still accessible from the selected car via links, so may be relevant.
When the HVAC control module receives a rear window defog request from the HVAC control faceplate, the HVAC control module will supply voltage to the relay coil. Battery positive voltage is supplied at all times to the relay switched input and the relay coil is always grounded. This allows battery positive voltage from the relay switched input to flow through the switch contacts and out the relay switched output to the rear window defogger grid.