Ignition Switch Circuit: Description
WARNING: This page is about a different car, the 2008 Toyota Yaris. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is turned to the ON position, the battery positive voltage is applied to terminal IG of the theft warning ECU. When the battery positive voltage is applied to terminal IG of the ECU while the theft deterrent system is operating, the warning stops. Furthermore, the power supplied from terminal IG of the ECU is used as the power for the door courtesy switch and position switch, etc.