As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, CREW NOTED THE MASTER WARNING LIGHT ILLUMINATED IN CONJUNCTION WITH THE LT ENGINE LOW OIL PRESSURE LIGHT. ADDITIONALLY, THE CREW NOTED THE LT ENGINE OIL PRESSURE INDICATOR DISPLAYED ZERO OIL PRESSURE. THE LT ENGINE WAS SHUTDOWN AND THE ACFT RETURNED TO THE DEPARTURE AIRPORT. THE ACFT LANDED SAFELY. MX DISCOVERED THE LT ENGINE OIL CAP WAS NO INSTALLED. THE CAP WAS REPLACED, OIL WAS SERVICED, AND SUBSEQUENT ENGINE RUN WAS SATISFACTORY.