Well the rings should be perfectly circular and should extend to the edge of the glowplug and the end of the wire should touch the shell of the glow plug itself. If you have a good glo igniter it will tell you if the glow plug is foul (the guage) Also, it should be bright enough so you can tell if its good. Charging your igniter would also help. The stock savage glo plug isnt that good I would go pick up some McCoy's or O.S. glow plugs. If you are breaking it in, be sure to run the truck rich, so broken glow plugs should happen. Its all for the sake of the engine.