Test both spark plugs and spark plug leads. With engine running place the wire in the cradle, slide it up and down the length of the wire. Flashes of light should be visible.
To test spark plug, place opposite end as close to spark plug boot as possible. Flashes of light should be again visible. Steady flashes indicate normal. Erratic or no flash indicates faulty component.
Length: 3.3/4" (95mm).