[jclark003]

Tach pickup should be on the flywheel housing left side. Unless flowscan is tied into tach signal probably not sender. If ground checks out possible you have fluxuating +vdc from key switch going bad. Install a jumper between +12v terminal (red wire) and run terminal (usually purple wire) will tell you if this is the problem. Just take care not to jump the start wire (maybe yellow and red wire) and also take note that engine will not stop with jumper in place.