I was trying to start my 2006 ram 2500 turbo diesel the other day with low batteries. the needles on the RPM and Speedometer were jumping around and then the speedometer needle went all the way around past the 120 MPH and stuck against the little peg that it normaly sits on when the truck is stopped.
Now the speedometer does not work. the needel just stays in that position???

 

Try running a gauge check/reset. Hold down the odometer reset button, switch the ignition to run and release the button. Hopefully that resets the stepper motor for the needle.

 

It would be interesting to know if it worked or not.