Q. "when you mentioned the tach on the trip started to cut out, did you mean the car started to die and would not run?"
A. Yes, it mis-fired and stumbled and the tach needle became erratic for a minute or so before quitting and would not restart. The tach is wired in series with the coil and when the tach circuit becomes "open" the coil is left with no voltage input and you are dead in the water.