Ignition Switch System: Notes
WARNING: This page is about a different car, the 2020 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.
The BCM controls the ignition modes, including OFF, ACC, ON and START. This allows some systems to be activated without starting the vehicle.
The BCM provides voltage at all times to the ignition switch. Depending on the ignition switch position, voltage may be routed to one or two of the ignition switch input circuits back to the BCM.