Ms Pacman wiring question

[razor1]

I'm restoring a Ms Pacman cocktail table and it looks like the previous owner used a weedwacker to wire it up.

I'm tracing back all the wiring to figure out what goes where and what cut wires need to be resoldered etc. The one question I've run into, which I know is a simply question, is how do I wire a "credit button" onto the machine. The coin acceptor wiring is trashed but the friend who this is for has asked that I install a button that will perform as if a coin was placed in the machine.

The pin outs for the PCB show one pin for each of the following:
Coin Meter In
Coin Meter Out
Coin Mech Switch
Credit Switch

Which ones do I need and which ones can I ignore? Also, how can a switch have one lead without a return lead? Does the ground act as the other lead?

Thanks.