I have this same question/issue..
Ive left my power supply hooked up as my Jamma Harness is slotted and numbered, and the ROMS work fine..
However the original Rampart 2 player controls seem to route or share leads with the 1player/2player buttons which route through the coin door.
So to save having to rewire all the buttons, and to have use of my coin doors for fun (or to bug my friends for their quarters

) Id like to hook the coin door back up ( I disconnected it from the harness before installing the JPAC for exactly the reason listed in the main thread)
At this point my joysticks and action button works fine, but I have no 2nd or 3rd button control. From what I can tell, its wired correctly to the harness, burt they are deactivated via the coin door being unhooked..
Mine is not a fancy door with lights. But it does have a test switch on it..
Any ideas?
Is there a way for me to possibly hook up my harness to the original Jamma board and put a mulitmeter on the coinbox somewhere to generate a voltage reading?