I had similar problems with my previous bird, a '68 convertible. The problem was the wire that taps off the battery that eventually powers all accessories and charging system. The wire was bad so I replaced it. Didn't completely fix the problem. The wire comes off the battery and goes to a connector on the passenger side firewall. My connector was badly corroded. I thoroughly cleaned the connector and then everything was fine. 99% of my electrical problems were due to oxodized, dirty or painted electrical connections.
