So, you put aluminum foil over each charge. All that foil makes you drool. Not really - it's hot, dry, and you have NO extra bodily fluids at this point. Now you run cables from the racks to the big board. The board has a bunch of holes in it, and a probe.
Probe touches the contact, and a shell launches.
You make sure everything is correct before showtime. Continuity check, is the technical term. For the continuity check, you send a few millivolts around, and see if everything is properly connected. Continuity check shows some problems, so you rewire, clean contacts, etc until it all works. Do the check, tweak, check, tweak, etc.