Have just replaced alternator on 740 turbodiesel. Could not get exchange unit readily so had to accept petrol engine alternator this does not have a terminal for the rev. counter, lack of which isn't a major problem; but is there any other way of picking up a signal for the rev counter. Also since old alternator started to die (early warning given by rev. counter erratics), the speedometer needle is also somewhat unsteady, this has not gone away with new alternator.
Can any body comment on what might be causing this, is it indicative of a further or related problem? (autoelectrics is not my strong area!)