As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PREFLIGHT WITH EMER LTS SWITCH IN ARM, THE AFT BULKHEAD EXIT SIGN AND THE UNDER LAV EXIT SIGN WILL NOT ILLUMINATE. WITH THE SWITCH IN ON, NO LIGHTS WILL ILLUMINATE. REMOVED AND REPLACED THE #4 EMERGENCY LIGHTS POWER SUPPLY WITH A NJA SUPPLIED REPAIRED UNIT OPS CHECKED SATISFACTORY, IAW AMM 33·50-06.