Well the Ipac 5V solution finally works for me (as long as NumLock is on)
Edit-> come to think of it... I had LEDs from Happs hooked in the machine I recently sold, but the coin return was actually square buttons I inserted "coin rejects" into. It was a last minute hack before he picked it up. The "numlock" requirement was the only remaining problem.
You could buy two hard drive LEDs with leads from MicroCenter. Cut them both in the middle and wire them together so there is one set of leads coming out. Reconnect that one of the black jumpers, and plug it onto the Ipac's LED header (either scroll lock, numlock, or caps lock). Basicly what I did but I bought the overpriced LEDs from Happs just so I could use those stupid white lamp holders.
For some reason the 5v and gnd on the LED header doesn't supply a full 5V?? Someone posted a diagram for rapid fire on the ipac. He's using the 5v from the LED header and one of the GNDs on the screw terminal. I'll give that a try if I get sick of making sure numlock is on.