If want to do a quick check to see if you actually have a dead glow plug, you could unplug the glow plug harness at the relay and use a test light hooked to your battery at each pin of the harness connector. If there is no light, then it's definitely bad. If the light goes on, the glow plug is generally working. Now I say "generally" because you really need to check the resistance or physically see it hooked to battery power as D-911 suggested to see if it's truly good. But in my experience 9 times out of 10 if the light is on, the plug is good.


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