Adding to SBs last line..
If one were to look at the power feed block diagram, you will see that the HFM ECU has to be powered up by the OVP, but once the engine is started , the OVP can actually be disconnected as
power is now supplied to ECU from engine supply [alt circuit]
So, unplugging an OVP with eng running is not a good test for OVP as the engine will still run w/o OVP.., but it will not start w/o OVP...
Thats why the common "No Start" OVP symtom and the little Tap-Tap relay trick...
..or there abouts..