I have a monster tach that is works when i t feels like it. when it is not showing the correct RPM's it is raising up to about 8k and it will just hang up there, then it will drop and raise back up.. Anyone have an idea of what could be wrong???

 

could possibly be hooked up to the wrong tach wire. do u have a tach on ur cluster as well? if so, do they match up? u could have something wrong wit ur dizzy.