I've been having trouble, but have been able to fake around it for a while with temporary wiring and leaving the coin door open so I have access to it. Now I really want to solve this but am stuck....
I have a two-coin-slot Williams style door and an IPAC. Each mech has a switch with three contacts. The rear contacts on the coin switches are commons, so I wired them together and then ran them to one of the IPAC grounds.
Now I previously had COIN1 and COIN2 buttons on my CP right next to START1 and START2. So I wired a short lead from the IPAC COIN1 terminal and connected it together on a female spade connector to the "NO" contact on one coin door switch. I then ran the CP COIN1 button to the male spade connector. This way I can disconnect the CP buttons but leave the coin door switches active by simply pulling the spade connectors apart.
Of course I did the same thing for the second mech and COIN2.
The problem? When the coin door "NO" is simultaneously connected to the COIN1 button, the button does not work. Disconnect the door, and the button works. Reconnect the door, and the button ceases to work. This is the case with both COIN1 and COIN2. Why?

I've also noticed that sometimes the coin switches act a little flaky. They commonly ignore a coin, but if I flip the switch manually, it registers. Sometimes they count 2 or more coins. (Robotron likes to see 4-coins for each one inserted). Seems like some games act differently than others.
Any ideas how to remedy this? A better way to wire?
TIA.