'92 Volvo 240 sedan 190k

Been having having this problem on and off for a while and its occurring more often (but not always). Sometimes I get dim dash warning lights. Perhaps happens more when its damp or maybe that's my imagination. The lights tend to go out if I raise the RPM. However, and this is what confuses me - it doesn't seem to be voltage related - I have a cigarette lighter voltage meter and it doesn't vary much between when the dash lights are on vs off. The car seems to charge fine and the voltage is 13.8-14.1V on the cigarette lighter voltage meter. When I start the car I see 12.5V at low revs until I rev it slightly and the voltage then rises - I think this is a characteristic of the alternator and exciter wire set up.

I've previously done a lot of research/diagnosis and reading the miriad of posts here but still can't figure this out. Replaced the alternator brushes, checked grounds,checker batter cables etc for voltage drops connections etc, re-soldered the cluster, checked the exciter wire and connections, and nothing helps. I thought the last time I changed the voltage regulator (1000 miles ago) had fixed it but the problem has re-occured and the brushes still look almost new. Really out of ideas at this point. Try an new alternator?