System Diagram - Vehicles without Adaptive Steering
WARNING: This page is about a different car, the 2019 Ford F-550 Super Duty, 2019 Ford F-450 Super Duty, 2019 Ford F-350 Super Duty, and 2019 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
Horn Operation
The BCM sends a signal to the horn switch through the SCCM and the clockspring.
The horn switch uses 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 into the steering wheel, it pushes down on the upper set of contacts, collapsing the springs, into the lower set of contacts. When the contacts touch, it signal from the BCM is completed to ground through the clockspring, indicating a request to sound the horn to the BCM.
The BCM then grounds the horn relay coil to energize the horn relay. When energized, the horn relay provides voltage to the horn, activating the horns.