Principles of Operation
WARNING: This page is about a different car, the 2007 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
Vehicles Without STX Package - Voltage is supplied at all times by the smart junction box (SJB) to the stoplamp switch. When the brake pedal is applied, voltage is supplied to the high mounted stoplamp and the multifunction switch, which routes the voltage to the rear lamps.
Vehicles With STX Package - Voltage is supplied at all times by the SJB to the stoplamp switch. When the brake pedal is applied, voltage is supplied to the high mounted stoplamp and the rear stoplamp.