Usually glow plugs are only tested by putting a test light to the terminals. The clamp will go on the positive battery post and the pointy end of the light will go on the terminal for each glow plug. However, this test is pretty hit-or-miss and the proper way is to check the resistance.
My friend and I were bitten by the resistance check though about a month ago. All glow plugs tested good on a cold engine. Once current was supplied to the glow plugs though, some would go open (no continuity through them and hence no heat) and he would have a hard start and rough running once it started.
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Tuning, PCM flashing, and burning chips for 7.3s since 2008. Repairing all aspects of 7.3L Powerstrokes for 25 years.
Eight 7.3L PSDs in the driveway including a 1994 Crown Vic and 1973 F100/2002 F350. Looking for the next victim.
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