As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NORMAL START TAXI, WHEN POWER WAS APPLIED FOR TAKEOFF, THE TAKEOFF WARNING HORN SOUNDED. THE TAKEOFF WAS REJECTED AT APPROXIMATELY 20 KNOTS GROUND SPEED. FOUND UPPER TAEKOFF WARNING SWITCH BROKEN INTERNALLY. REPLACED PER MM CHAPTER 31-20-24. (M)