300Tdi Tachometer - Testing and Replacing the Analog Signal Wire

Recently the 300Tdi embarrassed itself with aluminium shavings right through the engine bay and the tachometer flatlineing. Having replaced the alternator in the 2000's after experiencing a similar issue, the alternator was swapped out immediately. However the tacho' did not come back to life,...

I am well aware of the alternator's W terminal clip, and this is not the issue. The terminal clip is not the issue either, it's good. Having double-checked the Heller wiring diagrams many times. It definitely works, and the car has no charging problems. Leading to a much larger attempt to fix the tachometer problem.

Having purchased a 2nd hand dash cluster, and fitting out the old tacho unit, it seemed not to do the trick either.

- So I am just wondering if there is a way to re-wire the unit, just in case the old wire burnt up when the old alternator went?
- Is there a coloured wire on the back of the dash cluster, or does it go through the discovery's ECU computer?
Also:
- Is there a way to test the old taco unit to see if it is still alive?

Although a rather small problem, it's the only item that does not work on the 4x4 at the moment. So I hope there is a way to get it solved. Having owned and maintained the Disco for almost 30 years now, I don't want to give up on it.

What year is your Discovery

For model years petrol or diesel 1995 to 1998 diagram is below. Some 1994 MY models escaped with the 200 wiring.
Its a simple and straightforward feed (wihite grey) to the rev-counter from the alternator as the diagram shows.

The input to tachometer is in C207 pin 5, should be white/grey wire

may help