rev counter problems

hi i have a problem with my disco 1 300 tdi rev counter idling when shows low or no revs then at 70 shows over 4000 revs, is there a fix for the original binnacle or is it off down the scrapy?
its had a new alternator before i bought it in january have had a look at the wires and all looks good to me.also have put a new serpentine belt and belt tentioner when i changed the timing belt.
thanks for the help.

On mine it was the spade connector on the alternator .. remove it, replace with a new one, clean the alternator connector, job's a good 'un ..

Also, if you've bought the wrong alternator there might be 'timing' issues .. there are differing sizes of pulley wheel fitted to earlier and later disco models, so using the wrong one might still tension up OK, but may also give entirely wrong readings.

hi all have done some digging around on the disco, changed the spade terminal - no change. so went and got a second hand binnacle - problem solved works a treat now.