Circuit Description
WARNING: This page is about a different car, the 2002 Lexus LX 470. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is turned to the ACC position, battery positive voltage is applied to terminal No. I19-21 (ACC) of the body ECU and when the ignition switch is turned to the ON position, battery positive voltage is applied to terminal No. I21-2 (SIG) of the body ECU. See Fig 1.