I take the heads off to moves games down into my basement. I moved Super Mario Bros down. Got it assembled, plugged connectors where they fit assuming each connector could only go into the correct place, turned the game on and blew some stuff up. Turns out connectors aren't unique or keyed on System 3... I then figured out that most of the connectors were labeled and if I had actually paid attention, I could have saved myself a lot of trouble.