OK so mechanically if an engine is good all it needs to run is the wires that come from the ecu and go to the engine bay, right? I mean there is lots of other wires that go to stuff like head lights and tail lights but in theory if you unhook everything except the wires that go directly from the ecu to the engine and then crank the car it will start right? also i don't think there is a wire to the fuel pump but you could just run a switch with relay.

basically all a car needs is switches and a ecu to run. no main relay or other random wires.