If a "ballast resistor" is in place now and the points distributor is functional, then simply retain the primary side feed wiring as it is now. The red wire for the p-tron goes to the coil (+) terminal, the black wire from the p-tron goes to the coil (-) terminal.
If the oem ignition wiring currently uses a functional "resistor wire", then a ballast resistor is not used...but the resistor wire goes to the coil (+) terminal instead.
And all this is "assuming" that the installed ignition coil is the oem unit or a direct replacement of the correct primary resistance value (1.5>1.8ohms).