Electronic ignition and old tacho

Its hard to tell whats happened here because too many things appear to have been altered at once.
Before the electronic ign. was fitted was the tacho working?
Old tacho electrics do not like modern electronic ignition signals.
If it works with the points put back in then that could be the answer.
Some solve it by just buying a modern tacho and hang it somewhere, but if originality is called for then the tacho must be gutted and fitted with up to date internals. (about$200).

Hi mickos,  I think it would be good if you can fix the original wire and reconnect it. The reason is that it performs two functions. First when the key is turned to "on" 12 volts is fed from ignition switch thru the loop at the tacho and then connects to a resistance wire that is the correct length to reduce the 12 volts back to about 8volts that then connects to the coil. (you cant run a 12 volt coil continuously on 12 volts it will fry.)
Second when the points open and close they cause a "pulse"
or signal that travels back up the wire and can be read by the tacho as it passes thru the loop. (not hard wired). That why I think you should reinstate this wire.
Another problem is that fitting electronic ignition can change  the shape of this "pulse"so that the old tacho cant read it.
I hope this helps.
 

I put a H&H ignition dissy from the uk on the rs, the tacho still works and reads right but you have to rev the car a little when 1st started to get the needle going than its fine been like this for over 12 months. also had to put a relay on the dissy to get 12vs on start up the starter was sucking to much when cranking & i was only getting 8.5 - 9vs at the dissy making it a pig to start put the relay on 1st piston up hot or cold & brummmm hope this helps