an electrical nightmare , please help , 1972 dart

I wonder if you don't have a bad voltage regulator? They are pretty cheap. I actually had a bad one and didn't realize it until I replaced my gauges with a new cluster that had a voltmeter in it. You should be seeing something like 14 volts with the engine running and the alternator charging. The voltage regulator is mounted to the firewall and is kind of trapezoidal in shape. I tried to paste a picture here but it didn't work for some reason. With low voltage, turn signals will stop working and all kinds of goofy things will happen including your car will quit running when there isn't enough power for the ignition. This can happen with a good battery and alternator.

Good information regarding grounds ^^^^in the last post. I didn't want to duplicate that so please consider that as well.

I may have missed something in your initial write up and if so I apologize. Good luck