Quoted from pin2d:I'm sure it's been covered before but I can't find a thread
It's where the Tournament Start button goes.... It should have been on you machine when shipped from the factory...
They get removed often since they are in the way of removing the lock down bar (two wires for the light, two wires for the switch), the plug you see was in the goody bag, so that you could remove the switch and plug the hole.