Horn Operation

WARNING: This page is about a different car, the 2016 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

The horn switch consists of 2 sets of contacts separated by springs. The lower set is connected to ground and the upper set is connected to the horn signal circuit.

When the driver airbag is pressed, it pushes down on the upper set of contacts, collapsing the springs and allowing the contacts to touch. When the contacts touch, it completes the circuit and provides the ground signal which is routed through the clockspring, the SCCM and then to the horn relay, which is integral to the BCM.

The BCM supplies voltage to both the control coil and the switched side of the horn relay. When the coil is energized, the horn relay provides voltage to the horn, enabling the horn to sound. The BCM has the ability to provide a ground for the coil side of the horn relay, sounding the horn without requiring the horn switch to be activated.