VDO makes 12v automotive tachometers -- you'd need to find one in the saime diameter (52mm, or whateverr).

You can see if you can find a unt that will fit. Then you'll have to deal with the conectors. I'm not sure if it connects into a preterminated harness. You could probably figure-out however and just wire it yourself.

ARE YOU SURE THAT IT'S THE TACH and NOT the connection to the alternator or ground!!!!

Usually it's that and NOT the tach, Mike.