5. Press H.T. voltage button located on left side of indicator gauge and with other hand slowly open air control
needle valve located on right side of gauge.
6. Observe the gap sparking characteristics of the plug in mirror finish of gauge, while increasing the air pressure in
A. If electrode gap sparking characteristics are bright and continuous throughout gauge pointer rise from Red
Zone to Green Zone, the spark plug insulator is dielectrically sound.
B. If audible or visible Flashover is noted in the spark plug shielding barrel while the gauge pointer is in the
Green Zone and plug gap sparking characteristics are bright and continuous, the spark insulator is
Flashover in barrel is due to the presence of excessive high tension voltage which can build up sufficiently
to seek out any insulator defects (see note under operations) or discharge up insulator sleeve to grounded
C. If electrode gap sparking stops while gauge pointer is in Red Zone and flashing over in barrel is noted,
inspect insulator shielding barrel for defect or cleanliness. If found defective, scrap plug; otherwise, clean
barrel, recheck electrode gaps, and retest plug.
D. If electrode gap sparking stops while gauge pointer is in Red Zone and no flashing over is noted in barrel,
inspect electrode gaps for possible bridged gap, firing end cavity for cleanliness and possible cracked
insulator tip. If insulator tip is cracked or broken, scrap plug; otherwise correct possible cause for failure
and re-test. If plug fails to check out, insulator has internal defect. Scrap plug.
8. Release H.T. Voltage switch button, close air pressure needle valve, remove terminal contactors and plugs from