The emergency start is a momentary switch which activates a solenoid to join aux and start battery. There will also be a duel battery solenoid as well ( prob in engine bay). The dash switches are cheap crap which is surprising . Not a compressor it is a vacuum pump ( think sucking blood and vomit out of mouth). Don't worry it didn't go through the part you have,sucked into container further up the suction line .Don't get rid of the charger yet, I think you can run it on 110v but will loose half the amp output. Ask around your electrician mates. The big round plug with thread on it is NATO military speck power plug. Don't silicone the holes cause it can be acidic use something like body panel sealer . I reckon your fine new vehicle was a private ambulance probably mines . check the gutter rail for any damage from roof racks.