But testing with the meter doesn't always seem to work. I had glow plugs that tested fine yet failed to actually get very hot when hooked to a battery.

WARNING if you do this hold the glow plug with a pair of pliers. If not you will burn yourself pretty bad.

So far I am 2/2 I have two MB diesels and both needed a complete set of glow plugs.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200