For check of a spark plug works or not, not turning out it from a seat are necessary an awl and a "crocodile" clip, connected with electric wire.
Awl insert between a high-voltage cable and a rubber cap of a socket of the cover of the ignition distributor. A clip "crocodile" connect to earth contact of the car. If the spark plug (and a high-voltage cable) works normally after such connection the engine will start to work with faults. If the engine works without change, it is possible to do a conclusion that the spark plug (and-or the high-voltage cable) does not work. Such way excludes possibility of electrocution at check of spark plug (or the high-voltage cable) on the working engine.
By the way, the damaged high-voltage cable sometimes is shone if to look at the working engine in darkness
