As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED AFTER TAKEOFF UPON GEAR RETRACTION THE RED UNSAFE LANDING GEAR LIGHT REMAINED ILLUMINATED. EMERGENCY GEAR EXTENSION WAS PERFORMED WITH NORMAL INDICATION AFTERWARD. THE AC DIVERTED, MAINT FOUND PIN M OF THE RT DOOR UPLOCK SWITCH PUSHED BACK. THE PIN WAS REPAIRED, OPS CHECKS WERE GOOD AND THE AC WAS RETURNED TO SERVICE