(took awhile to find the old thread I detailed the method on)
To make an extreme example, imagine all the wires are the same color. You would have to mark the ends of every wire currently connected to the controller's outputs with a numbered tag. Then you would take resistance measurements from each wire to every other wire, one at a time, and write down the measured resistance value on a grid chart. That can be a lot of measurements (45 measurements for 10 wires) - but it will pinpoint which of the unknown wires is the common. Once you are certain of the common, you can work out the rest.
Thanks Wet Boots I'll give it a shot.