Ignition switch power on "run and start"

What ignition/distributor are you using? If using MSD, Hei conversion or other aftermarket ignitions, your "IGN1" and "IGN2" wires are normally twisted together, supplying the combined signal. Tap in from there, or better yet use that source to trigger a relay that will supply a clean 12v supply.
If using the stock-style Chrysler electronic ignition, use leads from IGN1 and IGN2 to trip a relay to supply the Sniper.