As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUTOPILOT WAILER HORN INOP. GROUNDED - YES. CONFIRMED, ALSO NO RED A/P WARN FLASH ON STATUS ANNUNCIATORS AFTER DISCONNECT. WITH GND APPLIED TO D299P PON 48 - A/P HORN SOUNDS. GOOD 28VDC ON PIN 53 FROM IFSAU REF B737-800 WDM 22-14-11 SH1 PG 2. REMOVED AND REPLACED MCP PER B737-800 AMM 22-11-34. PERFORMED GOOD INSTALLATION TEST AND LLM TESTS PER AMM 22-11-34-400-801. ALL REQUIRED TESTS PASSED. AUTOPILOT WAILER HORN OPS NORMAL.