Hey, I just bought 2 DB25 male to female cables and set them up to work with the Opti-Pac.
I don't have a Multimeter, after this discussion I think I know what it is...
Inside my cable, every wire was the same color. I cut the cable in half, stripped off the white outer casing from the ends, and stripped 2mm of the plastic from each of the 25 wires, on both ends.
I used scotch tape and marker to number each of the wires on one end. Then I connected the male/female ends of the cables together.
I held a 'aa' battery and a flashlight light bulb and mashed one end of the battery on wire #1 against my workbench and the lightbulb on the other end of the battery, and took the yet-to-be-numbered wires from the other end of the cable and brushed them along the lightbulb's side-contact, looking for the light to come on. When the light came on, I knew that I had found the other end of the wire, and I labeled it #1. I went ahead and did that with wires 1..25, until I had them all figured out.
Then I just took wire number 1, hooked one end to button 1 on the optipac, and hooked up wire 1 on the other end to the button. It worked perfectly the first time.
I suspect a multimeter is a tool designed for this purpose, and is probly a little less tedious. Took me an hour or two to find them all.
But I tell you, man, it's SWEET. Like everything with building your own arcade controls, it's TOO sweet. My mind baloons into all the great things I can now build, and I can't really quite keep up (especially when I keep losing precious time by playing all the games).
It's great, you connect one set of wires to the i-pac, and the other set to the controls, and you have a solid system for yanking apart controls and connecting a different one.
I sure wish there was a DB 32 or something... I need just a few more wires...
I paid $12 per 6 foot cable at Radio Shack.