alternator wiring with dedicated ignition circuit

I run a separate on/off toggle to feed battery power to a non stock electronic ignition in my '73 Power Wagon. As it is now, once started, I need to run with the ignition key in the "on" position in order to get charging juice back into the battery. The charging system is bone stock original with a new voltage regulator and rebuilt 60amp alternator. How could I redo my wiring to keep the charging system out of the old '73 wiring harness? I guess I don't want the alt. field to be hot all the time, right?

Thanks for any and all input, folks!