Hi all, I recently put in a under dizzy cap electronic ignition kit in a 1600xflow 78 model motor, it runs very well.
The face on the tacho i had in the dash was buggered and wasn't going as i rewired the ignition for the 12v coil, I just replaced with one i got off ebay.
I run the appropriate wires from negative on the coil to the tacho, the tacho ran well for about 1 min then began to read slow until it gradually stopped and now won't run at all. 
Have i Missed something like needing a resister in the wire from the now 12v system to the tacho ?
I have a old replacement tacho which i can make a good one out of the two if i have damaged it.
Any suggestions
 
Thankyou
 
Mickos

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).

Thanks Ron, yes the tacho was working prior to the change.
The resistance wire died and i had major dramas finding it so i rewired the ignition curcuit to 12v and put in the EI kit.
When you say old tacho's don't like the new signal is the new signal just to strong?
I could try putting a ballast resistor in the wire from the neg on the coil to the tacho, that should knock the signal back down to where it would have been with the old lower voltage curcuit maybe?
 
Thanks 
Mickos

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.
 

Thanks Ron, the system that is now installed states it needs the 12v circuit at all times and to bypass the resistance wire or it won't run. They make that very clear in the guff that came in the pack, the coil is also new and came in the pack.
I may just have to get a newer internals from a tacho and stick it in the old body.
The higher voltage on the coil is why i am thinking i need to cut that back down and it has fried the old tacho as it sits.
The kit I am using is this one but only for the 1600 
http://www.ebay.co.uk/itm/Ford-Pinto-Stealth-Electronic-ignition-kit-AccuSpark-Red-Sports-coil-Bosch-/170707787542?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item27befa1f16#ht_1439wt_1396
 

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

Thanks for the input Reg, i did get this problem sorted by replacing the internals in the original tacho with a cheap but new tacho, still get to keep the original look but new internals which seem to be handling the changes i made to the ignition with no worries.