Righto
Attach the green wire from your tacho to the black wire on the plug in this picture:
http://www.imagedump.com/index.cgi?pick=get&tp=466289
You can twist the wires together and tape them up with electrical tape, but I used a couple of wire connectors like this (you could also use some male-female crimps):
http://www.imagedump.com/index.cgi?pick=get&tp=466287
Next you will need to connect the red wire to the "on" wire on your ignition as shown here, it is a black wire with a brown stripe:
http://www.imagedump.com/index.cgi?pick=get&tp=466297
However there is another wire on the same plug as rev signal wire that works aswell as shown here:
http://www.imagedump.com/index.cgi?pick=get&tp=466298
I connected it the same way as the green wire:
http://www.imagedump.com/index.cgi?pick=get&tp=466286
You will then need to find an unpainted screw to earth the black wire onto.
Your tacho should work if you have installed it correctly following those steps.