As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING TROUBLESHOOTING OF UPPER BEACON SYSTEM C/B POPPING. C/B WAS PUSHED IN AND A NOISE WAS HEARD & SPARK CAME OUT FROM PANEL 426VU. FOUND TOGGLE SWITCH AT FAULT. TOGGLE SWITCH 2LV AT PANEL 426VU REPLACED IAW AMM 20-45-21 UPPER BEACON TEST C/O IAW AMM 33-48-00 SERVICEABLE.