Principles Of Operation

Horn

Principles of Operation

The Battery Junction Box (BJB) supplies the switched and control voltage to the horn relay (part of the Body Control Module (BCM)). When the driver air bag module is pressed, the horn switch (which is integrated into the driver air bag module) is closed and ground is supplied to the BCM (Body Control Module) which is routed through the clockspring. The horn relay then energizes, sending voltage to the horn, enabling the horn to sound.

The horn switch is not a single component, but consists of contact points located on the steering wheel and driver air bag module. The contact points are separated by springs. One set of contacts is part of the steering wheel itself and the other set is part of a metal plate mounted to the rear of the driver air bag module. Springs mounted to the metal plate are isolated by plastic seats on the steering wheel. When the driver air bag module is pressed against the steering wheel, the contacts on the driver air bag module and the steering wheel touch to complete the circuit.