Abstract: In an ignition indicator system for internal combustion engines, a transformer is interposed in each line between the spark plug and distributor or other timing circuit. The transformer has a sensor element positioned adjacent thereto to be indirectly coupled to the transformer output circuit. Terminal means is provided for connecting the sensor element to detector means which permits analysis of the pulses for firing the spark plug. Preferably, the transformer and the high voltage portion of the ignition system is shielded by a grounded casing or sheath to minimize radiation of signals, as well as to confine any explosion of ignited gases within the casing or sheath. Access to the sensor element does not adversely affect the shielding effect of transformer casing.