Tacho and electronic ignition.

Hi just trying to get my tacho to read correctly. I am running electronic ignition it reads about double.I know most people people get them recalibrated to suit.I've heard of people running a wire from coil to fix it .cheers

Factory Tacho needs a looped wire running through a ceramic block attached to the back of the tacho via a brass nut.  A lot of cars seem to be missing the white looped wire and put the coil feed straight on the back.  This is wrong