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 K9 Body Control Module detects the driver or passenger door is in the locked state, it will send a serial data message to the appropriate S79D Front Side Door Window Control Switch-Driver or the S79P Front Side Window Switch-Passenger which will provide the respective control circuit 4244 or control circuit 4245 with approximately 5 V which will illuminate the lock indicator.