Problem with 3.9V8 Rev Counter

I have a problem with my 1994 3.9V8, The problem started about a month ago with the rev counter acting funny, when i hit 2000revs it shoots upto between 4-5000 revs depending on the speed. The engine isnt racing. When i use anything electrical it then affects the rev counter. When the vehicle is at idle it doesnt appear to charge the battery as i found out when i was stuck in traffic on the motorway and the rev counter went to zero. Lucky it is LPG otherwise it would have cut out.
I had the alternator overhauled in June and i took it back to be tested today. It is working fine. The battery is quite old so i have also bought a new one today. It worked fine for about 2 miles and then started doing it again.
Has anyone any suggestions

Had identical symptoms on my 300 Tdi, it's not the alternator itself, it's a losse connector on the wire or wiring polug that connects to the alternator. Took mine off, removed the plastic connector, which had got very brittle and is a possible cause, added some decent connectors (soldered rather than crimped) connected the alternator back up and haven't had the problem since.

I'd also, while you're getting dirty, check the earth leads, if they look at all suspect, rusty,dirty, corroded, replace them ... for the price they're not worth messing with.

vehicle-wiring-products

is a good source for almost anything of this nature. (I know 'cos they're down the road from where we used to live and I visited them regularly when I had an S3)

Thanks Paul i will have a look although i took the alternator off today to get it tested and the wire looked ok. I will strip it back and solder it just in case.

Heh, mine also looked and felt OK ... it was only when i took it off that the wiring had corroded and turned into verdigris (green) that i realised it wasn't right ...

'course, it could still be summat else ...