The test that will give you the clearest indication of glow plug health is a test of how much current it is drawing. The newer type that connect in parallel (i.e. they all get 12-volts) should draw something like 12-15 amps. I had one that drew about 2 amps when hot. The difference is obvious. However, when cold, it was difficult to tell any difference between the good and bad by just reading ohms - since the resistance is so small anyway.

Thus you need a multimeter that can handle measuring this level of current.

I recommend the Tenma compact digital multimeter sold at MCM Electronics for $19.95

Go to www.mcmelectronics.com and enter as a "Guest". Enter "72-5095" in the product search and that should locate this meter for you.

This meter has the special 20-amp current measuring range that you need, and is reasonable in cost. It's what I use.

Ken300D