As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED A LANDING GEAR AIR GROUND FAIL MSG, LANDING GEAR WOULD NOT RETRACT ON TAKEOFF CLIMBOUT OF KORD. CREW RETURNED A/C WITH AN UNSCHEDULED LANDING TO KORD. MAINTENANCE INSTALLED GEAR PINS AND FERRIED A/C TO KSTL. MAINTENANCE INSPECTED AND FOUND BAD WIRE IN LEFT MLG NR 2 WOW HARNESS. MAINTENANCE THEN REPLACED THE LEFT MLG NR 2 WOW HARNESS, OPS CHECK GOOD.