Ignition switch power on "run and start"

.........And while you are at it..........consider powering the loads off that circuit through a relay.

Your 73 has/ had Stock Mopar breakerless? The two terminals at one end of the ballast are jumpered to gether. That is the "IGN1" "run" connection. The other one you want (IGN2) is normally brown and connected to the terminal of the ballast which also goes to coil+

The remaining terminal of the ballast feeds over to the original ECU and is no longer needed