For 1990-2009 cars

### Body Control Module (BCM)

A/C Switch: The scan tool displays On or Off. The BCM displays On when it receives an input from the HVAC control head indicator an A/C request.
Battery 1: The scan tool displays the value of the vehicle battery voltage.
Rear Defog Relay: The scan tool displays On or Off. When the BCM energizes the Rear Defogger relay, the scan tool will display On. When the BCM de-energizes the Rear Defogger relay, the scan tool will display Off.
Rear Defog Switch Input: The scan tool displays On or Off. When you depress the rear window defogger switch, the switch pulls the rear defogger switch signal circuit of the BCM low. The scan tool will display On. When you depress the switch again, the rear defogger switch signal circuit of the BCM will return to its normal state. The scan tool will display Off.