Glow plugs are gone at 540 hours

[ptsg]

Is there any sensor which commands when to turn it on/off? i could not find one. Sorry for the ignorance

There is actually two temp sensors on the engine. One for the instrument cluster and the other one is used for the glow plug controller so it knows the coolant temp and adjusts the preheating and after-heating times.

Here is a little graph that shows how much time it runs:

 

[ruffdog]

If the GPs don't shut off, I wonder if the problem could be the ign switch. If the ign switch activates the relay that turns on the GPs, maybe the SW is bad?????