Does anyone have a manual for the Irem Hook arcade game? I'm looking for the wiring for Player3 and Player4. It appears it is a 9 pin connector on the motherboard.
Didn't see a manual online... but shouldn't be too hard to figure out.
Locate the Ground pin and then ground each of the other pins and note the reaction of the player.
EDIT:
Or do as Oryk says.
(I didn't think to look for other Irem 4 player games)