Bit of a long shot, but does anyone have the little block and loop wire off the back of an Escort or Capri tacho?
like this one

 
I think my tacho is out of a Capri and it didn't come with the wire or block on the back.


 

Or is it possible to make up my own wire? Or is that little mounting block essential to the whole setup?
Something like this maybe?

The wire is just a simple double loop with no actual connection. Its the little nylon block with the metal top and sides that is the tricky bit. See the two metal bits either side of the threaded post on the tacho? Well the little metal piece goes over the nylon block and down each side touching those  metal bits forming a connected loop that allows the tacho to read the signal from the coil and work out the revs. It shouldnt be too hard to make that bit up, but there is more going on than meets the eye.
Here is some essential reading.     www.spriteparts.com.au      Look up tech tips and then on the side bar under tachometer.    Cheers,...ron.

Cheers for the info Ron. And thanks for the link.
I've been doing some reading on the interwebs today and found out just what you said. I need to make an "inductive loop" to go on there. Found a guy who made one out of a soup tin and a piece of plastic weedwhacker :)

Hi Pete
Pretty sure the old smiths tachos have the same block (MG leyland Hillman ETC).