Electrical gremlins again (crazy needle syndrome)

[Peter Orban]

Another vote to check out the alternator, even if it was recently rebuilt.
My son's car ('91Golf) had a recently rebuilt alternator in it and had similar problems.
As it turned out the first problem was that the filed wiring was not soldered in properly to one of the slip rings. In another year the soldering for one of the rectifying diodes let go.
Clearly shoddy workmanship.
The car was bought secondhand and came with the rebuilt alternator and starter.
I also had to fix the rebuilt starter, that was also nearly brand new, there was hardly any wear on the commutators.

Good luck, Peter