Crank Sensor

So where's the 5v source?

From what I've read, {true or not?} on a GM pin B is powered 5v in the run position only. During cranking or below 400 rpm the ECM opens the relay bypassing the EST signal from the computer allowing base timing. That would require killing power to pin B, which seems to indicate the reference is powered from another source, the 12v input. The ECM would still require the reference signal to read rpm {400 or less command} regardless of pin B's on/off status.