Start..no run *resolved*

the ignition box depending on type
can
1) disconnect the coil from ground causing it to switch off and make a spark, simple, effective

2) pump supply voltage to the coil negative which means both primary + connection and primary - connection are at supply voltage and the coil will be off.... 12v both sides = coil not on.
less simple but achieves the same outcome

Tacho
if it connects to the coil negative with no external adapter boxes or anything like that it is the basic standard set up used by many. It is triggered from the 200-400V back emf in the primary as the spark is unleashed from the secondary of the coil. the collapsing field that creates the spark in the secondary also makes a tiny version of the same effect in the primary the result is a backwards pulse of 200-400 v

for the tacho to impact the operation of the coil it needs to be the wrong type or have shorted out or broken down inside or its wire has a short to ground....

situation 1 if the tacho or its wire has shorted out or a capacitor in it has failed it could be acting as a ground in which case the ignition box can not switch off the coil and you have no spark. if a capacitor has failed it might fail as a short from one plate to the other... it will have some resistance. and the impact of the short may vary depending on if other capacitors in the circuit are still operational and are changing up under these exceptional circumstances.

situation 2
the short in the Tacho causes the situation where the ignition module takes the coil negative to supply voltage to switch it off but it can't because the coil negative is connected to a short to ground in the tacho hence the coil stays on all the time and gets very hot. expect to fry you ignition box.

you can cause a tacho failure by plugging a 12 volt or 5 volt square wave signal driven tacho into coil negative and exposing its circuitry to the 200 volt spike.

some of them designed to be driven by a tacho signal from ECU or expensive ignition box. NOT the 200-400 volt spike off the coil negative.

you are the second person i have known to have had a "NO start" due to a problem with a tacho that previously worked fine, in the last couple of years, and id never even heard of that as a thing in 35 years as a car hobby kinda guy...

Dave