Been playing in the Troll and found my dash rheostatswitch wasn't working. I checked the other rheostatswitches on the navigator's side and they were fine. I had a spare one in the garage and it wasn't working either. Then I remembered a tip given to me by AlexW and stood them in vinegar for ten minutes. I was using Aspall's Organic Cider Vinegar but I guess others will be the same. Took them out and dried them and they work fine.
Following up Mr Burts point why bother with one, I was wondering also why a lot of old cars have a separate switch for the dash lights from the exterior lights? surely you always want the dash lights on when you have your exterior lights on and power consumption is negligible, similarly I cannot recall ever thinking the dash lights on the V4 were too bright and needing turned down.