charging needle waiving back and forth

[customcruiser72]

My charging / volt meter needle has started waiving back and forth erratically. It goes from extreme Discharge to extreme charge and the needle moves so fast back and forth you can barely see it. The problem is intermittent and sometimes the needle is steady in the middle. It has been doing this for a few weeks and my battery has not been discharging and it is a daily driver. I thought it was the guage but recently I was driving in the dark and my headlights were alternating bright/not so bright. I have an external regulator which has been replaced a couple times over the last few years. I think I will either convert to internal regulated altenator or get a new external regulator but I was wondering if these symptoms are familiar to anyone.
I have a 71 GMC Longhorn C20 with a V8.