If you touch the probes together you should get a steady zero, or close to it. Do you by chance have it set on voltage? That'll give you funny readings if there's no voltage. Also if you meter doesn't auto-range, make sure you have it on the right range...you're only measuring 1 Ohm. Just for fun, get a light bulb and put one lead on the metal tip and the other lead on the threads, that'll give you some resistance.

If you can get your hands down by a plug, but one probe on the back end where the wire connects, and the other probe on the engine block (anything big and metal on the car can be a ground) or on the body of the plug. That will directly measure the resistance across the plug.

Then check the wires, one probe on each end of the glow plug wire.

Good luck

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now