GM Service Manual Online
For 1990-2009 cars only

The fog lamp relay in the underhood accessory wiring junction block controls the fog lamps. The coil side of the fog lamp relay receives voltage at all times through the fuse output-battery circuit. The common terminal of the fog lamp relay also receives power from the fuse output-battery circuit. When the fog lamp switch is set to the ON position, the Body Control Module (BCM) supplies a ground through the fog lamp relay output-coil circuit. This energizes the fog lamp relay, turning on the fog lamps by sending power to the normally open switch contact and the fog lamp feed to the fog lamps. The fog lamp feed also supplies power to the indicator lamp in the fog lamp switch. The fog lamps receive ground from G101 through the fog lamp relay output-coil circuit. The BCM will turn off the fog lamps when the headlamp dimmer switch is turned to Flash-To-Pass (FTP) or if the headlamp switch is in HEAD and the headlamp dimmer switch is set to HIGH.