IF the wiring is the same as a MSD 505/6/7 type box:
One wire is the on/off. On the MSD is was a small gage red wire. Autotronics suggested removing the factory positive wire from the coil and attaching connecting it to the MSD on/off wire. They even supplied a plastic insulated strip and a couple of tabs to make this a neat job - and reversible.
The real power for the CD ignition came from the car's battery. Mine and probably most mopar folks attached with a ring terminal at starter relay. Actually I've just changed that but that's not important. Any location wit ha really good connection with 12 or 10 ga wires to the power will work.
When the key is in run or start the MSD on/off wire gets power. it doesn't need a lot of current. As far as I can tell, it powers a internal relay that connects everything else internally to power from the big red wire.
