Kick harness question

[DasFool]

I'm working on building a kick harness and control panel switcher for 4 button and 6 button games. I'd really like to just use common ground for all of the buttons because it would make the switching a lot simpler and I am wondering if there's a strong reason to use the kick harness ground for buttons 4, 5, and 6 instead of the common ground from the PCB like the rest of the buttons. Any help would be appreciated.

[antron]

For CPS1 and 2 I believe it is the same ground.

[DasFool]

I would assume that the ground is the same unless for some reason the game board has it's own power supply. Then the ground for the cabinet PSU and game PSU would be different, right? My electrical knowledge is somewhat limited...