Let's run down the basic list again..............
Good battery
Properly adjusted valves
Glow plugs in good shape
Diesels use compression to fire, are you using a good quality engine oil?
Once the glow light is off, the relay is off, the glow plugs are off. In other words, crank the engine about halfway through the glow cycle.
What kind of cold weather are you experiencing? How many miles are on your car? Do you have good compression?
What turns on the glowplug light? I assume its the relay, but how does it decide to turn on the light?
There is a switch on the thermostat housing that senses coolant tempature and will adjust the amount of time the relay sends current to the glow plugs.
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I have heard of GPs testing OK with an ohm meter and still not getting hot. The only real way to know is to remove them and apply 12V through jumper cables or one of those "jumper packs" and see if the tip glows bright orange.
Take a look here.
http://www.dieselgiant.com/glowplugrepair.htm
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