As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: SPEED TRIM FAIL LIGHT ILLUMINATED. FLIGHT AIR INTERRUPTED BACK TO CLT. FOUND STABILIZER TRIM CUTOUT SWITCH IN CUTOUT POSITION CAUSING SPEED TRIM FAIL LIGHT. CREW VERIFIED THEY DID NOT MOVE SWITCH. REMOVED AND REPLACED STAB TRIM CUTOUT RELAY.