Problem that has annoyed me for a decade. My voltage gauge always reads low. My multimeter shows my battery at 13.4-.6v at idle and around 13.2-3 with AC engaged.

My gauge however will show about 12.7 at idle and about 11.5v with AC on. Even less with lights on etc. It's always been this way but I know my charging system is fine and I know the gauge is known to be quirky. Is there anyway to recalibrate it or even pull the needle and reposition it to a more accurate location? At this point I just may buy a new gauge unit as my temp gauge sometimes will peg and get stuck at 12 o'clock when I turn the ignition off. I know these 2 share a ground. Is it possible a corroded ground could be the culprit?