The BCM start messages via CanBus, not straight wire to the ECM, ECM checks to see if it's ok to run the starter (not in gear, etc). I have no idea within the BCM what happens but as long as you hold the key in START, the starter will run. To me that says it's continuousWhat I haven't found, is how does the ECM get the request to crank?
Where/how does the switch send the request? Is it a momentary signal to the BCM then sent via data cables/can bus? Or wire straight to the ECM?