Need to find switched 12v wire that's hot while cranking & with key in ON position

As abodyjoe mentioned where is the wire that was connected to the + side of the coil origionally?

Use that wire. put a voltmeter on it with the key on and you should get voltage. Also as Joe mentioned you will need to bypass the ballast resistor so you get the full 12 volts to your new syst. (By bypassing the ballast, I mean hook the wires from both sides of the resistor together)