Easiest way is a multimeter. See which wires have extremely high resistance and you’ll figure out which one is bad with a lot less mess and effort. You’re also supposed to pull the glow plugs out hot. Not cold.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k