Some of the pins on the JAMMA connector aren’t on the board. These are only ground pins on the pinout, and so far everything works okay. It’s still a great project, though, that turns old ...

Back in the day, and by that we mean the late 80s and early 90s, arcade machines started using the JAMMA standard ... The usual way of wiring in a joystick and buttons is with a wiring harness ...