As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED. ON TAKEOFF, AS THE POWER WAS COMING UP, THE MASTER CAUTION LIGHT ILLUMINATED. PILOT REDUCED POWER AND THE LIGHT WENT OUT. REJECTED TAKEOFF AND TAXIED CLEAR OF RUNWAY. PERFORMED INSPECTION AND DEPARTED ORD. NO MAINTENANCE INVOLVEMENT. OPERATIONAL CHECK GOOD.