no when they go bad they usually just stop working,
the alternator gauge "dancing" sounds like a short or loose wire somewhere
they can be a pain to find, you just have to be persistent
The alternator needle only dances when it starts to go out. when you keep your foot on the gas a little bit its fine (actually a lil on the positive side buts its always been like that) but when it starts to go out or if your off the gas and a rpms go down it dances then the motor stalls out