Smiths Rev Counter Diagram Wanted

[Bert Palte <palte@gmx.net>]

Hi fellow listers,

The electronic rev counter on my 1972 Sunbeam Sceptre doesn't work any 
more, though it was functioning when I drove the car for the last time (in 
1985 that was...).
Apart from the bezel it is similar to that of my 1970 B.

Does anyone know where to find a wiring diagram for a Smiths rev counter?
I do have a background in electrical enginmeering, but without a diagram it 
is still a hell of a job.

Thanks

Bert
1970 MGB (European specs)