[dimeified]

My tach is accurate for the most part but now and then it would go nuts and fly up and bounce all over the place. At the same time, i noticed sometimes my clock wouldnt work during the day. Sometimes at night the clock gauge lights wouldnt light. That was my clue that there is a grounding problem with the tach and clock. I replaced the ground from the clock to the tach. Problem was still there, so obviously the ground problem is at the tach to whatever grounds it. After moving the tach around in and out of the dash i havnt had a problem since. Im going to remove the big rectange plug from the back of the tach, and spray contact cleaner on the plug receptacles and make sure that the contacts are nice and tight. I would try the same if i were you.

I should mention, i had replaced the voltage regulator thinking it was that when the bouncy tach started.