As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NEW C-172S ON CROSS-COUNTRY FLIGHT, OIL PRESSURE STARTED FLUCTUATING. OIL TEMP NORMAL AND NO LOW OIL PRESSURE LIGHT ILLUMINATION. OIL PRESSURE GAUGE STARTED FLUCTUATING OFF SCALE LOW. PRECAUTIONARY LANDING MADE. MAINTENANCE FOUND OIL PRESSURE GAUGE CONNECTOR PLUGGED INTO GAUGE, BUT NOT LOCKED OVER LOCKING TAB. RE-CONNECTED AND OPERATIONAL CHECKED SATISFACTORY.