Circuit/System Description
WARNING: This page is about a different car, the 2008 Pontiac G5 and 2008 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
The body control module (BCM) monitors the ignition 1 signal, Accessory signal, and the OFF/Run/Crank signal from the ignition switch. When the vehicle operator places the ignition switch in the Off, Accessory, RUN or CRANK position, the switch supplies B+ to the BCM appropriate input terminal.