Trailer Parking Lamps
WARNING: This page is about a different car, the 2018 Lincoln Navigator. 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.
When the parking lamps or headlamps position is selected, the BCM provides a ground path to the BJB parking lamps trailer tow relay (non-replaceable). When the BCM provides ground the parking lamps trailer tow relay, the relay is energized and the relay provides parking lamp voltage to the trailer tow connector.