Yeah I had already found it. I will try it tonight.

Which ignition system did you install that caused issues with the tacho? When I had the TB42, I removed the points and put in a Petronix unit. I didn't have any issues with this, but it sound like you put in something with a bit more kick.

I'm not sure why these tacho's are so picky, I would have thought the circuit would be simple ... just a frequency counter triggered by the falling edge of the signal wire. Maybe levels are not high or low enough .. or duty cycle? I need a CRO to analyse the signal from the ignition coil VS. the converter I have.