[TheSecondChris]

It sounds like a jerky gauge. I saw a post recently from the youtube mechanic Edredas in North Carolina where he wrote "A lot of these cars read a little over 12v on the gauge despite being about 13.9 at the alternator while running. They will also show under 10v when not running despite having 12v at the battery. I think it's mostly due to age, but its rare to see one behaving properly. Thanks!"

As a starting point, I'd recommend getting one of those cheap digital voltage gauges that you can leave plugged into your cigarette lighter and you can drive around for a couple weeks and compare both readings.

I replaced my VR on my '84 last year and yes the brushes were work and the new part helped a little bit. I've cleaned a lot of grounds too so at this point I'm convinced that my alternator output is lower than it should be and a replacement is warranted. When my headlights are illuminated along with the cooling fans I can see the battery light glowing a little bit. I mention this to you because the cost of a quality Bosch voltage regulator is about $45 and in retrospect I wish I'd put this money towards the purchase of a rebuilt alternator.