glow plugs not working

[juleshs]

when i turn the ignition on my glow plugs do not warm up i have to do it with a seperate switch conected to the battery.I have changed the relay still no joy its a95 aaz

[AudiVWguy]

Your gonna have to get a test light and trace the power from the big fat wire where the power starts, through the relay, and back out to the glow plugs. The power gonna stop somewhere in line.

[Smokey Eddy]

One of the sensors in the coolant T thing at the top of the head (at least for my engine) tells the relay to shut off if it things the engine is already hot and the GP's never actually turn on.
This sensor could be faulty? Try unplugging them both and see if that makes a difference?
An easy test that i dont honestly think will solve your issue but it's definately worth trying... takes all of 30 seconds