Principles of Operation
WARNING: This page is about a different car, the 2007 Lincoln Mark LT and 2007 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The fog lamp switch is integral to the headlamp switch. When the fog lamp switch is engaged, voltage is routed to the fog lamp relay coil, which then energizes and routes voltage to the fog lamps. The fog lamp relay coil uses the high beam circuit for ground. When the high beams are turned on, the fog lamp relay will not energize.