What causes the glow plug light on dash to not work? (1982 245 D24)

[chad1966]

(1982 245 D24)
What causes the glow plug light on dash to not work and the glow plugs?
It happened last week out of the blue.
I visually inspected the wiring and nothing seems to have broke or fallen off. Yesterday the GP light came on 1 time just randomly after coming out from the store midday.
I put a new #13 fuse in.
I believe there is a GP temp sensor at the back of the head.
Is it the female terminal that sits roughly in the middle of the rear timing belt? If it is getting a bad connection would that signal that the engine is warm/hot to not turn on the GP?
It will start in the AM but only after I give it a little fuel for about 5 seconds and than it will idle on its own.
This is defiantly not what has been the case from the time that I bought the car.
It usually starts right up to an idle.
The only thing that I have changed is that I am currently just about through my first tank of B50.
I dont think that that should affect the GP though.
Any help is appreciated. Thanks.