So I started my 83' yesterday and the chime started going off at 50% speed, intermittently. I also noticed that the built in volt meter was only sitting at 10v instead of its usual 12v. That was odd but none of the warning lights had come on and the engine wasn't behaving or sounding any different, so I took it for a quick spin around the block. Everything works fine until the tachometer hits ~4000 RPM. This magic number is where the chime goes off at full strength, the tachometer drops to zero and the voltmeter drops to zero. It continues this until the engine hits ~4500 RPM, or I clutch in, where it goes back to not chiming at all or the 50% intermittent, and the tachometer working like it should.

Just to eliminate a few things I checked both my coils, and both ignitors. They all seem happy. My alternator is putting out 13.4v.

Is this a grounding issue/ do I have a short somewhere?

Has anyone else experienced this? I'm still pretty new to this cars guts, so any info/ best guesses would be greatly appreciated.