As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO MIA DUE TO SPEED TRIM FAIL LIGHT ILLUMINATED AT 18,0000 FEET. THE AIRCRAFT LANDED SAFELY AT MIA WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED MAIN ELECTRIC STAB TRIM RELAY R64 PER FIM 22-13-00-810-818 AND WDM 22-13-11.