I believe the tacho works, I just bought it from ahspares.co.uk, it seems strange if they sell tachos that arent calibrated, it looks completely new. What strikes me is that it shows around the same as the previous MG 4 cyl tacho that was in the car, thats why i was thinking of the wiring could be wrong. Or a long shot, is the engine running that fast, atleast it makes alot of noise when going at that speed.
I better find a tool to check the ignition, I believe they can measure the revs. too. That should make it somewhat easier to solve the problem.
Niels