Headlamp Switch
WARNING: This page is about a different car, the 2016 Ford Transit-350 HD, 2016 Ford Transit-350, 2016 Ford Transit-250, and 2016 Ford Transit-150. However, it is still accessible from the selected car via links, so may be relevant.
The headlamp switch monitors the knob position. When the headlamp switch detects the knob is in the HEADLAMPS ON position (or a fault with the headlamp switch), it sends a message over the LIN circuit to the BCM, indicating the headlamp switch position or a fault with the headlamp switch input.