Cranks but won't start. Unplug ground at field spade on Alternator and it starts?

340sFastback said
1969 Barracuda
All wiring is factory specs

New alternator and voltage regulator worked for two weeks then developed a no start issue.

Coil gets 8 volts when cranking. If I disconnect ground on spade connector on two week old alternator car gets full voltage at coil and fires immediately. I had local parts store order stock replacement alternator. What showed up was a two spade field alternator and I ground one spade to alternator body which worked flawless for two weeks. NAPA '69 stock replacement voltage regulator.

I get some pics tomorrow. But its a stock wiring stock replacement parts setup. I do have Unilite distributor been on there for 14 years and it gets power for Ignition 1 side of ballast resistor. Unilite igntion module and MSD High Vibration coil mounted in stock bracket on manifold.

Like I said in orginal post, new alternator and voltage regulator were fine for two weeks. Stopped to get gas all the sudden no start issue occurred.

Starters draw down the battery voltage during cranking to about 8 volts. The points ignition systems were designed to function on about 8 volts, so that during cranking you had full spark. That is why Mopar vehicles are famous for their ballast resistor. The run position of the ignition switch supplies voltage to the one end of the ballast, while the other end supplies the 8 volts to the coil + terminal. The start terminal has a wire that supplies cranking battery voltage to the coil + terminal.
Supplying the coil with running battery voltage would burn the points quickly.
Mopar coils have two primary terminals, 1 + and 1 - that goes to the distributor.
Some use a different coil (Ford) that had a ballast resistor built in and 3 primary terminals, 1 + batt, 1 - to the distributor and 1 start that gets volts from the start terminal on the ignition switch or from the starter.
Do you have 8 volts at your coil while cranking? Is there continuity in the wire from the ignition switch start terminal to the coil? Strange it worked for 2 weeks and then pooped the bed.