Six button Jamma harness and jpac

[Jenksie]

Hi all,

I'm looking to own a mame machine in a full size wooden arcade cabinet. I've found a supplier of the cabinet and getting my hands on a mame pc with jpac shouldn't be difficult.

My issue is that the cabinet comes with a 6 button jamma harness rather than using a kick harness. I've asked in a few places on the internet for advice which seems to vary.

The issue is that buttons 5 and 6 are on pins 26 and 27 which would ordinarily be unused and ground.

It has been suggested by several people that I cut these wires and wire straight to screw terminals on the jpac. The next issue is what to do with the ground. Will I need to split an existing ground to pin 27 for it to work and what happens with the ground on the screw terminal as the extra buttons are daisy chained with other buttons to the jamma harness.

I've searched extensively and can't find anyone else that's done this.

I'd appreciate any advice that can be offered.

[mgb]

If you're gonna use the jpac, to me it would only make sense to snip those wires for buttons 4 and above and terminate them on the jpac.
you can jump the common from the jamma connector to the extra jpac buttons

[danny_galaga]

Button 4 can remain, it's wired on the jpac, 5 and 6 are the ones left out.

[Jenksie]

If you're gonna use the jpac, to me it would only make sense to snip those wires for buttons 4 and above and terminate them on the jpac.
you can jump the common from the jamma connector to the extra jpac buttons

Thanks for the advice.
Sorry for such a newbie question but what do you mean by 'jump the common'?

[mgb]

Newbie questions are fine. It's how we learn things.

The ground screw terminals on the jpac for the extra switches should be electronically the same as the black wires on the jamma harness so you should only have to worry about cutting just the single wire to each switch and leave the common connections on the switches as they are.

When you get the jpac, you can confirm with a multimeter be testing resistance between the GND terminals and the existing black lines to the switches

[Jenksie]

Newbie questions are fine. It's how we learn things.

The ground screw terminals on the jpac for the extra switches should be electronically the same as the black wires on the jamma harness so you should only have to worry about cutting just the single wire to each switch and leave the common connections on the switches as they are.

When you get the jpac, you can confirm with a multimeter be testing resistance between the GND terminals and the existing black lines to the switches

That's great. Thank you very much for your help.