As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE BATTERY BOX FOR THE LEAD ACID BATTERY INTERFERES WITH THE LEFT MAGNETO HARNESS AND CHAFES THE HARNESS LEADS OVER TIME. THE INBOARD , FORWARD CORNER IS THE POINT OF CONTACT. I HAVE SEEN THIS SITUATION IN MANY 172S. ELECTRONIC MAGNETOS LIKE THE SUREFLY HAVE THE SAME PROBLEM DUE TO THEIR SHAPE AND SIZE. THE REPLACEMENT OF THE LEAD ACID BATTERY WITH A LITHIUM AND ITS ASSOCIATED SMALLER BATTERY BOX ELIMINATES THIS PROBLEM.