Horn System: Overview Mercury Sable V

Principles of Operation

Note. The smart junction box (SJB) is also known as the generic electronic module (GEM).

The smart junction box (SJB) supplies the switched and control voltage to the horn relay (part of the SJB). When the horn switch (part of the steering wheel) is pressed, ground is supplied to the SJB through the clockspring. The SJB then energizes the horn relay sending voltage to the horn, enabling the horn to sound.

The horn switch is part of the steering wheel and sits behind the air bag. There are two sets of contacts on the horn switch that are separated by springs. One set of contacts is connected to ground and the other set is connected to the horn signal circuit. When the driver air bag module is depressed it pushes on the top set of contacts and collapses the springs. When the springs collapse, it allows the contacts to touch and completes the circuit.

The SJB provides a momentary ground to the horn relay when the anti-theft system is armed, and an on then off ground when the panic button is pressed on the integrated keyhead transmitter (IKT).

Normal Operation

The smart junction box (SJB) supplies the switched and control voltage to the horn relay (part of the SJB). When the horn switch (part of the steering wheel) is pressed, the switch closes and ground is applied from the steering wheel switch harness through the clockspring to the horn relay through circuit CRH02 (BU/WH). The horn relay is then energized, applying voltage to the horn through circuit SRH01 (YE/RD), enabling the horn to sound. Ground for the horn is supplied through circuit GD123 (BK/GY).

This pinpoint test is intended to diagnose the following

1. Fuse
2. Wiring, terminals or connectors
3. Steering wheel switch harness
4. Horn
5. Clockspring
6. Horn switch (part of the steering wheel)
7. SJB

The smart junction box (SJB) supplies the switched and control voltage to the horn relay (part of the SJB). When the horn switch (part of the steering wheel) is pressed, the switch closes and ground is applied from the steering wheel switch harness through the clockspring to the horn relay through circuit CRH02 (BU/WH). The horn relay is then energized, applying voltage to the horn through circuit SRH01 (YE/RD), enabling the horn to sound. Ground for the horn is supplied through circuit GD123 (BK/GY).

This pinpoint test is intended to diagnose the following

1. Wiring, terminals or connectors
2. Steering wheel switch harness
3. Clockspring
4. Horn switch (part of the steering wheel)
5. SJB