That is usually a ground wire (green) but it kind of looks like a buss fuse holder. The kind on old C.B. radios in the power cables.
I would suspect that is a ground wire for something like a control panel. The ground wire so your user controls work, joy stick, start, fire, etc.
It could be for another board in the cab.
In any case I would turn off all power and unplug the game and follow/ohm out that wire to find out for sure. If it is a ground it should beep *again with power OFF* from that wire and a good ground (case of power supply or - side of cap on board.