Problem with 383 distributor, (earthing issue?)

This may have been mentioned before - you CANNOT troubleshoot electrical issues properly without a voltmeter/multimeter. It's a basic tool, like a set of wrenches.
you sound like me. WHAT YOU NEED to troubleshoot these old girls electrically

1...A multimeter. Try to get something better than Horrible Freight. For around 5-80 bucks you can get some decent quality, still China built. For the same price if you are careful you can get a "previously owned" Fluke 70 series. I HAVE 5 OF THEM although I use them for more than automotive

2....A 12V test lamp. I prefer a "real" light bulb type but the LED ones can be useful.

3...Although VERY useful is an old stop/ tail lamp socket and an 1157 or 1034 bulb. You can wire this many ways for different purposes

4....At least 2 and better 4 alligator clip wire leads. You can buy these various places, ebay, or you can buy alligator clips and make your own. Also very useful sometimes is a rag-tag clip lead long enough to reach from the battery to any other point on the car, IE from front to back

I am big on voltage readings AND NOT continuity or "ohm" (resistance) checks. This is because in cases of losing power, often switches or connectors "can check OK" under the low power of an ohmeter, but stop functioning under heavier functional load.