Start..no run *resolved*

Footnote 2?

How about this: The power wire to the spark box broke. With an electrically unknown (at that point) lump now connected to the '-' of the ignition coil, might the signal the tach was then subjected to have damaged it? That would make the two failures NOT concurrent but sequential.

Someone can test that. Have your rig running and cut/disconnect the BY wire to the box. Let me know if your $400 tach gets burnt. ...all in the name of science yanno.