Ignition Switch System: On
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.
When the ignition switch is in the ON position, the switch routes voltage through the ACC-designated and ON-designated circuits to the BCM. The BCM interprets this as the ignition on mode.
The BCM communicates the ignition mode to the other modules by sending an ignition status message over the CAN and activates the internal run/start relay, providing ignition power to the various vehicle systems and modules.