ECM Power Source Circuit [09/2014 - 11/2017]: Description
WARNING: This page is about a different car, the 2017 Lexus RC 350, 2017 Lexus RC 300, 2016 Lexus RC 350, 2016 Lexus RC 300, and 2015 Lexus RC 350. However, it is still accessible from the selected car via links, so may be relevant.
When the engine switch is turned on (IG), battery voltage is applied to the IGSW terminal of the ECM. The output signal from the MREL terminal of the ECM causes current to flow to the coil of the semiconductor pwr integration ECU (EFI-MAIN relay), closing the contact and supplying power to terminals +B and +B2 of the ECM.