Principles of Operation

Horn

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

The SJB supplies the switched and control voltage to the horn relay (part of the SJB). When the driver air bag is pressed against the steering wheel, ground is supplied to the horn relay coil 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 the contact points located on the steering wheel and driver air bag module. There are 3 contact points that 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.

When the vehicle security system is armed, the SJB provides a momentary ground to the horn relay control side to indicate the system is armed, and an on and off ground when an intrusion is detected or the panic alarm is activated.