I see a few incorrect comments here. I realize you fixed your starting problem. That said, a ballast resistor can certainly be used. In
fact, Pertronix recommends adding one in certain situations. To say it won't work with a added resistor is just plain silly.
Pertronix Ignitor kit for a NAA Ford is # 1244A, IF used with a 12 volt system and negative ground. It calls for primary resistance on the
coil of at least 3 ohms. NO ambiguity here.
An OEM Ford coil that came on a Jubilee/NAA has a primary resistance of 1.17 ohms. If that tractor is switched to a 12 volt system,
usually a 1.8 to 2 ohm ballast resistor is added to the OEM 6 volt coil. That comes to total resistance of 3 ohms (or more) which is the
minimum requirement for the Pertronix.
Pertronix simply has two requirements for the Ford four-cylinder engine. Primary resistance MUST be at least 3 ohms and it does not matter
how you do it. Also, there cannot be too much resistance that causes primary voltage to ever drop below 6 volts.
I note that I the NAA I just worked on. It was still a 6 volt system, but had a 12 volt-only coil someone added so it had weak spark with
the old points system. Then the owner changed over to 12 volts and added a ballast resistor and it still had weak spark. If that resistor
had been left off, it would of been fine. This however, was just a mess of mis-matched parts.