As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE. PILOT EXPERIENCED A HEAVY ODOR OF SMOKE IN COCKPIT. AVIONICS BUSS 2, AND ALL ASSOCIATED SYSTEMS FAILED DUE TO THE AVIONICS BUSS 2, 15 AMP. CIRCUIT BREAKERS TRIPPED AT THE SAME TIME. PERFORMED "ELECTRICAL FIRE IN FLIGHT" CHECKLIST. ODOR CONTINUED, RETURNED TO DEPARTURE AND MADE AN UNEVENTFUL LANDING. INVESTIGATION REVEALED THE TAIL NAVIGATION LIGHT WIRE HAD CHAFED THROUGH BY ONE OF THE RUDDER CAP SCREWS AND SHORTED TO GROUND. FOUND A CIRCUIT BREAKER FAILED TO TRIP, CAUSING THE NAV LIGHT WIRE TO GLOW, AND SHORT.