•Erratic or no flash indicates faulty component.
•With engine running place the wire in the cradle, slide the tool up and down the length of the wire.
•Flashes of light should be again visible.
•To test spark plug, place opposite end as close to spark plug boot as possible.
•Tests both spark plugs and spark plug leads.
 

•Erratic or no flash indicates faulty component.
•With engine running place the wire in the cradle, slide the tool up and down the length of the wire.
•Flashes of light should be again visible.
•To test spark plug, place opposite end as close to spark plug boot as possible.
•Tests both spark plugs and spark plug leads.