As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER LEFT ENGINE WAS STARTED AND DURING THE MAG DROP TEST, ELECTRICAL SMELL WAS DETECTED AND ARCING COULD BE HEARD. THE MAGNETO SWITCH WAS REPLACED AND THE AIRCRAFT RETURNED TO SERVICE. A SUBSEQUENT INSPECTION OF A MAGNETO SWITCH REVEALED THAT IT WAS INTERNALLY SHORTED. NO RECORD OF WHEN THIS SWITCH WAS LAST REPLACED, BUT THE DATE ON THE SWITCH WAS 77-04.