What was found
WHILE IN FLIGHT THE LEFT ENGINE RPM READING BECAME ERRATIC, GOING FROM NORMAL TO PAST RED LINE QUICKLY BACK AND FORTH. PIC PRECAUTIONARY SHUT DOWN ENGINE AND RETURNED TO HOME FIELD. AFTER TROUBLESHOOTING IT WAS FOUND THE LEFT HAND TACH GENERATOR SENSOR PLASTIC CANNON PLUG QUICK CONNECT HOUSING WOULDN'T TIGHTEN ADEQUATELY AND WAS GIVING ERRONEOUS READINGS. IT WAS NOTED THAT THE TACHOMETER SENSOR PLASTIC CANNON PLUG QUICK CONNECTOR JUST SCREWS ON BUT DOES NOT LOCK AS DESIGNED AND THERE IS NO PROVISION TO SAFETY WIRE IT SO AS TO NOT LOOSEN IN FLIGHT OVER TIME.