As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX - AIR TURN BACK - FLT 0803 - CREW REPORTED THAT THE LT MLG UNSAFE AND DOWN LIGHTS, BOTH RED AND GREEN, REMAINED ON WHEN GEAR WAS UP AND WHILE IN FLIGHT. CREW RETURNED TO PHX AND LANDED WITHOUT FURTHER EVENT. MAINTENANCE REMOVED AND REPLACED THE LT MLG UPLOCK SENSOR. OPERATIONAL CHECKS WERE GOOD IAW BOEING 737-300 MM 32-61-31.