2004 SR Johnson 2-stroke 40, 50HP Service Manual, Page 127Get this manual
IGNITION SPARK PLUGS
Blocking Diode Test
The diode is located in the engine harness tan wire circuit
SPARK PLUGS
Remove and inspect the spark plugs for the following conditions: Worn electrodes Cracked insulator Dirty spark plugs Replace all defective spark plugs1Diode
Disconnect engine harness 6-pin Deutsch connector containing the tan wireCalibrate ohmmeter on appropriate scaleUsing jumper wires, connect meter between engine harness tan lead and engine harness 6-pin connector terminal 6Note readingReverse meter connections or press polarity buttonNote reading very high reading in one direction and low reading in the other direction indicates diode is good
Before installing the spark plug lead cover on the spark plug, apply light coating of Electrical Grease to the ribbed portion of the spark plug ceramic and to the opening of the spark plug coverSee table below for recommended spark plug data and gap setting