an electrical nightmare , please help , 1972 dart

Bad connections. I would suspect the bulkhead connector. When connections are corroded, they can arc and cause all sorts of issues you are describing. Original wiring harnesses now have a lot of miles & weather on them. I had issues with my Duster when I bought it and replaced some of the wiring to resolve. Take your time and be methodical otherwise you'll be chasing your tail instead of locating the problems.