Hi to all, Help advice wanted!

Hi
I am new here, but not to terranos!
I joined as i am having problems with my 1999 automatic terrano 2. It has been in the garage for 2 weeks the problem is the rev counter is at o when i take my foot off the pedle, but it also cuts out on me. They fitted a new sensor in the crank, but no joy. re wired part of it, thought the govener was sticking when i was breaking, still no joy! Now they are saying the alternator has gone and will be expensive and i shoild get rid I have had 10 years problem free motoring so i am willing to try a few things but feel like i am getting nowhere. Has anyone else had this problem!
Hope anyone can put my mind at rest.
Joanne