OK, back on subject.
You have ignition switched power that was feeding your old HEI. Take that wire and splice in the "I" wire off the solenoid. The "I" is a secondary output off the solenoid to power the ignition while cranking the engine. Originally a bypass to the ignition ballast resister. With the ballast resister removed in an unknown manor by an unnamed shop they may have accidently deleted the bypass "I" wire.
So put the ignition wire (the voltage regulator wire works as well) and the "I" together and that will power the computer in run and crank. Just resplicing what someone unspliced sometime ago.