GM Service Manual Online
For 1990-2009 cars only

The control to the left of the steering wheel on the instrument panel also controls the fog lamps.

(Fog Lamp): When using the fog lamps, the ignition must be on and the parking lamps or the low-beam headlamps. If the high-beam headlamps are activated or flashed, the fog lamps will turn off.

Pull the exterior lamp adjuster control out to turn the fog lamps on, and push the control in to turn the fog lamps off. The indicator light in the knob will come on when the fog lamps are working.

Some localities have laws that require the headlamps to be on along with the fog lamps.