Rev meter issues.

The rev counter in my 1995 disco 3.9 v8i is rather pointless at the moment as it either:

1. reads 0 revs.
2. Moves Erratically.
3. Sometimes it works fine.

Ill add here that the engine runs perfectly and Idles perfectly. So the rev counter doesn't relate to what the engine is doing.

Any ideas?

Alternator connection. The wire that connects to the alternator is loose, or more precisely the connector is, or it's dirty. Unclip the wire, remove and replace the connector or try just cleaning it and crimping it back on.

What he said ^^^^^^