Circuit Description
WARNING: This page is about a different car, the 2003 Lexus IS 300 and 2002 Lexus IS 300. However, it is still accessible from the selected car via links, so may be relevant.
If the ignition switch is turned to the ON position, battery positive voltage is applied to terminal T5-10 (IG) of the theft deterrent ECU. Furthermore, power supplied from terminal T5-10 (IG) of the ECU is used as power for the door courtesy switch, and position switch, etc. See Fig 1.