I am having trouble with my alternator for the 4th or 5th time in a year. I'm running a 90 with 200tdi conversion and completed a chassis swap 2 weeks ago (but the problem started last summer). The first time it happened I drove a 200 mile journey and a couple of days later the alternator stopped charging. The next time it stopped I had driven through water 3 feet deep a few days earlier, so put it down to this. Then it packed in during normal day to day running. It has just packed up again after completing a 500 mile round trip over the weekend. Each time previously I had the voltage regulator changed which sorted the problem, and finally bought a new alternator but now the same problem again. The problem always starts with the battery light coming on very dimmly and infrequently until it is on all the time, only still dimmly, and then the battery becomes too flat to start the engine. It may just be coincidence that it packed up after long journeys twice, but I don't understand why the voltage regulator would keep blowing under normal circumstances.

Sounds to me like the alternator brushes are goosed, and not making a good enough contact with the slip rings of the rotor.

The brushes take field power INTO the rotor.

Generated power comes out of the stator windings.

This means the thing does not charge enough, because despite the regulator trying to put more leccy into the rotor, it doesn't work, so the regulator gets all uppity.

Did they fit NEW brushes and make sure the slip rings are clean and shiny?