my ipac 2 has a set of onboard pins that are used for LED usage that mimic the scroll/caps/num lock key LEDs (an LED harness can be bought from ultimarc.com to use these pins, but I didn't buy/use this harness). Anyway, I just used two of those pins (one 5V and the other ground) to hook directly to the rotary interface.
hope that's clear, if not, I'll try to post pics if you need...