As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING RUNUP AFTER ANNUAL INSPECTION, LT MAG WAS NOT WORKING. FOUND INSULATION ON P-LEAD WIRE WAS DETERIORATING AND SHORTING TO SHIELDING CAUSING MAG TO BE CONTINUOUSLY GROUNDED NO MATTER WHAT SWITCH POSITION WAS. REPLACED SECTION OF P-LEAD AS REQUIRED. THIS WIRING IS DIRECTLY ABOVE EXHAUST AND DETERIORATION WAS PROBABLY CAUSED BY HEAT OF EXHAUST SYSTEM OVER TIME.