Discovery engine speed sensor

[Guy]

Hi - I have a problem with the tacho on a 97 Disco 1. The needle sometimes works normally, sometimes drops and comes back up again - loose connection type problem.
I have a gnerally ok (Haynes) manual that says the engine speed sensor is in the bellhousing but its not there (its in the section detailing the sensors present on the model with the electonic diesel controller which isn't mine) - it obviously has one (which I suspect has an intermittent fault) but I can't find it! I would appreciate any help locating the thing and if anyone has found a solution to a similar problem.
thanks

 

[joey]

the tac info comes from the Alt... There is a small wire on the back that provides tach info... check in first, but I would also have the Alt itself checked, it may be going bad.