Abstract: A runway lighting system comprises a series runway transmission line providing current to a plurality of runway lamps. A failed lamp indicator (FLI) connects across the terminals of each lamp to determine when the lamp is malfunctioning. When the FLI determines that a lamp is malfunctioning, the FLI transmits a malfunction signal, during a specific time period defined in lamp address circuitry in each FLI, onto the existing series runway transmission line. A circuit status analyzer (CSA), which forms part of the vault computer, receives the malfunction signal, noting the time period during which the signal was received. The CSA then accesses an internal ROM look-up table to determine which FLI sent the signal.