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Herman's Amp gauge is showing red when travelling with lights on and when indicators are used Amp gauge moves!

So it looks like a new Alternator is required

thing is what type and is it the same for a BB M30 as a SB M20 engine?

any ideas?

I would just rebuild it. New bearings, brushes, regulator and perhaps even the slip ring.

Dunno if Alpina used special parts, can't imagine why. But yup, it may even be that just a fresh combo of brushes and regulator (available as one kit) is more than enough.