I had a problem the other day with my tach doign something similar, but it was all of a sudden. I was putting on my intake, and somehow the tack was stuck all the way over in the "pegged" position. Tried disconnecting battery, and no luck... I thought I may have bumped something in the engine compartment...
So I took the bezel and loosened a few of the clear plastic screws, then with a drinking straw I was able to flip it back around... Works fine now....
Weird...