GaRCField,
Unfortunately if that is what you were taught then they didn't go far enough. I never said to use a plug that didn't pass your tests, because if it doesn't glow or electricity won't flow through it then the plug is bad. But, if this is all you are relying on you could very well put a bad plug right back in to your engine. Because like I said above, a bad plug can still pass ALL or your tests.

Ken