Parking Lamps
WARNING: This page is about a different car, the 2018 Lincoln MKC. However, it is still accessible from the selected car via links, so may be relevant.
The BCM monitors the headlamp switch position by sending voltage signals on multiple circuits to the headlamp switch. There is one circuit for each headlamp switch position. At any given time, one of the signal circuits is switched to ground to indicate the headlamp switch position.
If the BCM detects a fault from the headlamp switch or loses communication with the headlamp switch, the BCM turns the parking and headlamps on. This is normal behavior of the BCM when a fault has been detected with the inputs from the headlamp switch.
When the BCM receives an input requesting the parking lamps on, it provides voltage to the parking lamps and the headlamp LED park/signature lamps.