I have a 96 disco and the tach will work some time and some time it will just jump all over the place could this be a vacuum line or any ideas to fix this? My truck is a 5 speed if that helps at all.

 

Check for a loose wire on your alternator, which is where the tach signal comes from. If the wires are good, your tach is starting to fail, kind of a common problem with Rovers.

 

I just replaced my alternator not to long ago so everything should be good. Would I have to get a whole new instrument cluster and if I do would I be able to make the miles the same as they are on my truck

 

Well when you get more acquainted to auto parts and their reliability, you will learn that brand new out of the box doesn't mean it will work and if it does, for how long.
That being said, go to your local auto parts store and have them do a free check.

 

With that being said,and oldbelt slipping can cause the same problem.Had this same issueon aBenz, replaced the belt, and all was fine.

 

Thanks alot for the help I replaced the belt at the same time I will get the alt. checked

 

If you wind up getting a new instrument panel you can get one from here.
http://www.roverlandparts.com/index....p;Category=264
As for making the miles the same, I used a drill attached to the speedo cable, that was on a old Oldsmobile, but it worked.

 

These are electronic. Your VSS reads pulses off the transfer case....