Abstract: A diagnostic system for rapidly trouble-shooting safety system induced shutdowns of production facilities such as combustion systems. A passive monitoring interface apparatus is mounted at the combustion system which includes a detector network coupled with the power source of the combustion safety system itself to provide an interface output condition representing the circuit status of each electrical contact. An identifier component is incorporated in the interface apparatus along with a connector assembly. The detector network may be manually programmed utilizing a terminal strip and jumpering to accommodate it to wide range of safety system circuit architecture. The apparatus further includes a connector for coupling via flexible cable with a portable interrogator assembly which is microprocessor driven and incorporates non-volatile memory retaining the configuration data associated with each numerically identified interface apparatus.