As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED WHITE SMOKE APPEARED FROM UNDER DASH BY BRAKE HANDLE FOR 3 SECONDS JUST BEFORE SHUTDOWN. THE ISSUE WAS TROUBLESHOT TO FAILED DIODES IN THE VOLTMETER CIRCUIT. THE DIODES WERE REPLACED IAW THE WIRING DIAGRAM MANUAL, SEC 2. THE OPERATIONAL CHECK OF THE VOLTMETER WAS SATISFACTORY AFTER THE WORK WAS COMPLETED. NO FURTHER SMOKE NOTED.