Not 4 ohms, but more like 1/2-3/4 (0.5-0.75) ohms. If you find a glowplug is 4 ohms, then it's on the way out.romie wrote:4ohms for each plug yeah?
Best test, as said many times on the forum, is to remove each glowplug & test across a battery, when you'll see the tip glow red hot. Initially, a good glowplug for the TD will draw nearly 20 amps, dropping to approx 12 amps as it heats up. Best not to hold it in any way, as it gets hot, and also takes a little while to cool down again. You'd need an ammeter that reads 20 amps to test an individual glowplug - many multimeters only go up to 10 amps.
In the past, I've tried measuring the current between the glowplug's busbar, and the battery, but I haven't found the figure on the ammeter to be very conclusive as to whether 1 glowplug has failed or not. Nowadays I test them individually. You can of course, measure their resistance in-situ, but you need to disconnect the other glowplugs, and it can be difficult getting a good contact with the multimeter's probes (if that's how you do it).
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I once had three glowplugs fail overnight, turning a first time starter into a totally dead car.