NOT familiar with that setup. What is the pump... CAV or Bosch?
But, in general, if there IS an electric shutoff, you SHOULD be able to hear at least a faint "click" when putting power to it.
Put a test light in series between the 12 Volt source and the terminal on the shutoff and see if the at least light, proving that the solenoid coil is not "open".
I DOUBT there is a way to mechanically override it.