The rear window defogger system consist of the following components:

Battery positive voltage is supplied through the DEFROSTER fuse, in the ISU, to the rear window defogger switch. When you start the engine, and depress the rear window defogger switch, the ISU energizes an internal relay. This allows battery positive voltage from the ISU to the rear window defogger grid. When you start the engine and press the rear window defogger switch, the defogger cycle lasts for 15 minutes.