[Early_S_Man]

Jamie,

It sounds like your CDI-unit caused the initial problem, and is continuing to fry any tach that you feed that high-Voltage signal to ...

I believe there has to be some conductive corrosion or contaminant causing a 'sneak current' path from the high-Voltage section of the CDI-unit over to the TD signal output terminal! I don't believe that the TD signal should be above 10 Volts or so! Do you happen to recall just what the highest Voltage signal peak that you saw was ... ??? It does not surprise me that hooking up a new CDI-unit to tachs that had already been fried ... didn't magically fix your problem and cause a good tach reading to reappear!