Circuit Description
WARNING: This page is about a different car, the 2004 Lexus IS 300. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is turned ON, battery positive voltage is applied to terminal IFSW of the ECM and the ECM and the EFI main relay (Marking: EFI) control circuit in the ECM sends a signal to terminal MREL of the ECM, switching on the EFI main relay.
This signal causes current to flow to the coil, closing the contacts of the EFI main relay and supplying power to terminals +B and B2 of the ECM.