Tachometer spun 360 and now sits under pin
 

3rd Gen 2006 5.9l 24v Cummins I6 HO Turbo ETH. Just replaced batteries with two Odyssey Extreme AGMs. Cleaned all cable connections and grounds. Alternator checks out ok.

I started the engine and the tach worked fine for about 5 minutes then when I took the RPMs to about 3k, the needle took off and spun 360 and hit the underside of the pin. I tried a gauge reset, and it went through the whole process but didn't work. All gauges reset except tach. Now when I drive my truck and accelerate, the needle moves but in the opposite direction off the underside of the pin (counter clockwise) to about 4k then returns to the underside of the pin.

I'm hoping someone is familiar with this problem and has a fix. Any solid known causes and real solutions will be greatly appreciated.

first of all, that's not a gauge reset, re-calibration or anything of that nature, it's just an actuator self test to determine if all the actuators and lights are working.

As for how to fix it, take the cluster out, take off the clear plastic cover and just spin the needle back with your hand, it'll be fine.

This video is about repairing a broken peg, but it might provide some useful/helpful information to you about what's going on in there.