I don't know what colours they are or anything but what I think based of the smiths one I got working on my mini is that the wires are probably:
1 power
1 earth
1 positive signal from dizzy
1 negative signal from dizzy
1 power for connecting up the little light that lights up the tacho when your headlights are on
the other wire I don't know about
Is there any other stuff like shift lights etc one or more of the wires could be to connect up this sort of parafinalia
what I would do being very careful not the disturb things too much is I would take the tacho apart. The first thing I would look for is the earth(s) these will tend to be connected to screws or other similar earth points.
OK so mark your earths
I would then try to sort out which one is the primary power the wire is probably a similar length and guage to the earth it is also probably red. (earth is black)
I would then try to find the globe that illuminates your tacho when the interior lights are on this funnily enough will be connected to a globe somewhere, chances are the globe will be somewhere where you can get to it incase you have to change it. The other side comming from the globe is going to be an earth so it may help if you try to trace it back to the earth you recognised earlier to confirm or deny this.
OK that has all bar 2 or 3 named two(I think) of the other wires are going to be for the signal coming from the dizzy and returning to the dizzy (the other option is it could use just one of these signal wires but as you seem to have too many wires I am guessing there are two signal wires)
The other wire that is left? well I don't know it maybe a seperate earth for the illumination globe that we identified earlier
So saying I am not an auto electrician(I just try stuff) and if you try something and blow up or stuff your tacho bad luck I am just suggesting stuff cause you didn't seem to be getting too far with it.
Well that's my bit of 2 cents
