First thing you need to do is figure if your ignition switch works like the modern A bodies. This is part of the key to the whole thing, as GM and Ford both used a resistor bypass circuit using the (Ford) fender mount solenoid, or (GM) the starter mount solenoid.
Chrysler did this different, here is the "deal."
The modern Mopar ign. switch has main power "always hot" into it.
Outputs are:
ACC---hot in "run" position or "accessory" position.
IGN1--the "run" terminal, hot ONLY in "run" position, DEAD in start!! THIS is what feeds alternator field (on 70/ later), The VR, the ignition system, electric chokce if used. It is the ONLY switched 12V in the engine bay
START: This is hot only in the start position, and feeds to the starter relay to activate it and then the relay activates the starter solenoid. It is also part of the neutral start circuit. The second small terminal of the start relay needs to be grounded, and that goes down to the center terminal on the neutral/ reverse light switch on the automatic. On stick cars 70/ later, it goes to the clutch safety switch
69/ earlier stick shift cars, that terminal was grounded, and not used as such,
NOW the ign resistor bypass, IGN2. This terminal, like the START terminal, is only hot in "start" BUT IS A separate circuit. IT goes to the coil + side of the ballast resistor (same for points or Mopar ECU) and is the ONLY source of power during starting. REMEMBER I noted above, that the "run" line goes DEAD in "start."
You should consider NOT feeding loads directly off an old ignition switch "run" terminal, but, rather, using that terminal to trigger a Bosch style relay, and feeding the loads off that
