Principles of Operation
WARNING: This page is about a different car, the 2006 Mercury Montego, 2006 Ford Freestyle, and 2006 Ford Five Hundred. However, it is still accessible from the selected car via links, so may be relevant.
The horn relay (part of the smart junction box [SJB]) receives the control and switched voltage from the battery junction box (BJB). When the horn switch (part of the driver air bag module) is pressed, voltage is supplied to the control (coil) side of the horn relay through the relay, to the clockspring and to ground. When the SJB detects the horn pad is pressed, the SJB energizes the horn relay which closes the switch and supplies voltage to the horn, enabling the horn to sound.