X-11 connector (model year 1991-1992): This connector is usually found in the engine compartment. It is a 16-pin round socket with a locking mechanism. To connect the diagnostic tool, you will need an adapter cable that fits this connector.
HFM socket (model year 1993-1995): The HFM (Hot Film Mass Airflow) socket is a 38-pin rectangular connector that is usually found in the engine compartment near the throttle body. It can also be located under the dash, behind the glove compartment. You will need an adapter cable to connect a diagnostic tool to the HFM socket.
If your 1992 Mercedes-Benz 500SEL does not have either of these connectors, it is likely that it does not have an onboard diagnostic system.