As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING GROUND RUN-UP PRIOR TO TAKEOFF, AS PILOT CYCLED TO RT MAGENTO, ENGINE ATTEMPTED TO CUT-OUT BUT PILOT WAS ABLE TO KEEP RUNNING BY SWITCHING MAGNETO SWITCH BACK TO "BOTH". FLIGHT CREW RETURNED TO RAMP AND SQUAWKED ACFT FOR DEAD MAGNETO ON RT SIDE. MX PERSONNEL REMOVED RT MAGNETO FROM ENGINE TO DISCOVER MAGNETO COIL LEAD TERMINAL END HAD BEEN BROKEN OFF FROM THE ATTACHED POINT AT THE POINT ASSEMBLY.