I find a Ignition switch wiring for the ECU and nothing for the Starter motor. To start the engine, can we directly power the Starter motor and ECU will automatically recognize that is cranking and start it?
The ECU has nothing to do with the starter circuit on the engine. When the ECU is powered up it looks for an RPM. When the engine begins to spin, the ECU makes decisions about the fuel and ignition (and everything else).