Circuit/System Description
WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.
When the S78 Turn Signal Switch is placed in the HEAD or PARK position, ground is applied to the Turn Signal Switch park lamp switch ON signal circuit to the K9 Body Control Module (BCM). The park lamps will also be signaled on when the Turn Signal Switch is in the auto position during night conditions. The BCM responds to the park lamp request by sending a serial data message to the K219 Lighting Control Module. The Lighting Control Module responds by applying voltage to the park, tail, and license plate lamp control circuits illuminating the park, tail, and license lamps.