Vanity Lamps
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
The interior lights fuse supplies battery positive voltage to the BCM. The BCM then applies battery positive voltage to the vanity lamps through the inadvertent power supply circuit. When the vanity mirror cover on the sunshade is opened, its switch closes providing a ground circuit, and the vanity lamp illuminates.