As you have said JZZ30 and JZA80 both use 'Fuel Pump ECUs' and as such the JZZ30 engine ECU was able to control the JZA80 fuel pump ECU fine

JZX100 uses a COR (Circuit Opening Relay) for the fuel pump control and as such this won't work with the JZA80 fuel pump ECU (as you have also said!)
My advice, I'd use a relay and the Power FC / JZX100 engine ECU 'FC' pin so that +5V is sent to the fuel pump ECU when the FC pin is Grounded and nothing is sent when the FC pin is not Grounded. I.e. connect one side of a relay coil to +B and have the other side of the relay coil triggered by the Power FC, 'FC' fuel pump control pin. Wire the relay so that it switches +5V to the Fuel Pump ECU on the wire that used to connect to the JZZ30 engine ECU FPC pin (the FPC pin connects to the 'pump speed control' input pin of the fuel pump ECU).
I'd use the +5V that powers the TPS, MAP sensors etc as the +5V to send to the fuel pump ECU.
Some info on my wiki that may also help...
http://wilbo666.pbworks.com/w/page/4...pening%20Relay
http://wilbo666.pbworks.com/w/page/4...20COR%20Wiring
Cheers
Wilbo
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