As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LT INTAKE ILLUMINATED IN FLIGHT. QRH COMPLETED, NOTIFIED DISPATCH/MECHANIC. LT AC GEN OPS OK, LT. APPEARS TO CYCLE EVERY 2 MINUTES OR LESS. AIR RETURN TO DTW. MAINTENANCE SWAPPED THERMISTORS (2 AND 3 WITH 4 AND 5) IN DEICE MODULE. RAN A/C FOR FIFTEEN MINUTES WITH INTAKE HEAT ON. ALL CHECKS GOOD IN DRY AND WET CONDITIONS. VISUALLY INSPECTED ALL DUCTS AND HEATING MATS, NO DEFECTS NOTED.