Street cruiser electrical problem?

Guys, just looking for some ideas here. Not a 429-460, but you guys like cool Fords.

I have a '67 Ford Fairlane GTA. 390, auto, 3X2 carbs, small hyd cam (unknown specs, just a little bumpy idle). It has a stock distributor with a Pertronix Ignitor electronic conversion with an MSD Blaster 2 coil.

Problem started a few weeks ago. Driving during the day was fine, but at night with the lights on it would die at redlights or anywhere it was just at idle rpms in gear (was ~700 rpm). When it died it was like turning the switch off. No miss, no skip or stutter, just shut off. I checked the voltage at fast idle in park and it was showing almost 15.5V. Had the alternator checked and it was good. Good voltage and it made 53 amps (this is a 55 amp old style Ford alt)

I replaced the external regulator and it brought the voltage down to 14.5 and 13.5-6 with the headlights on. Problem is better with the new regulator. It would idle in gear with headlights on low without dying. But, if I switched to high beam headlights, it would shut off again. I raised the in gear idle up to about 800-850 and that solved the dying with high beams.

But, it will still shut off if I turn on anything with high amp draw like the heater/ac blower fan. Turn the fan on at idle with or without the headlights on and it dies. Going down the road it's fine.

Ideas?

Have you had the battery tested? Other than that it sounds like the Petronix module is shutting down due to (what it thinks is) low voltage. Maybe a weak coil?

Are all of the grounds good? Batt to chassis/chassis to engine/dist to engine block? I also had trouble before with a Blaster coil. The screw that holds down the brass terminal for the coil wire backed out. I had no idea, but the coil wire was loose. Tightening it up solved the problem. That screw being loose will also allow the oil to drain out if it is mounted on its side.

Sounds like a ground issue.

my 69 mustang had trouble kinda like that.it was the ignition switch.the plug on the back was even getting hot and a little crusty.worth a look.