As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING GROUND RUN, LT ENGINE WOULD NOT RUN WITH THE LT MAG SELECTED. MAINTENANCE CREW FOUND THE BREAKER POINT ARM BROKEN OFF DURING INVESTIGATION. THE MAGNETO WAS REPLACED WITH A SERVICEABLE UNIT, AND THE AIRCRAFT WAS RETURNED TO SERVICE, MAGNETO TSO 425.0.