[Oldsguy]

It may not be possible. Usually the harness goes through a hole in the firewall and on the inside is actually terminated in the fuse block. You would have to be able to pass the complete assembly through the hole (however large it is) in the firewall and that may not be possible. To do that you would have to disconnect ALL the wires on the fuseblock that go to anything in the interior of the car. So you end up disconnecting as many or more wires in the passenger compartment as you would in the engine compartment. I think it would be better to disconnect at the engine.