I know all the MSD units I have installed has both coil primary wires come right from the MSD box. So even if you leave the ballast hooked up it wont be feeding anything. The MSD should get a 12 volt key on wire that needs power when cranking also. Then the 2 primary wires to the coil and two wires to the dist pick-up if using that style dist and the two heavy black and red wires go right to the battery. Ron