Audio Front Control Module (ACM) Illumination
WARNING: This page is about a different car, the 2012 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
The base (AM/FM) ACM has a hardwired illumination circuit from the Body Control Module (BCM). For all other ACMs, the illumination signal is received from the BCM via the MS-CAN.