System finally up.
You will want to check fuses 18 and 20 for the glow plug circuit. Here is the diagram. CLICK HERE
As you see in the diagram, the power goes from fuses to the timing control unit and then to the relay. If the fuses are good, then I would check the timing control unit. There is a few checks on it to check for power as well as to see that it is getting an input signal from the engine coolant sensor. CLICK HERE to get an understanding of how it works as well as what to check on it.
Hopefully it is just a fuse problem because the timing control unit can be a pain to work with. If you are getting the signal in, but nothing out, the timing control module is bad and needs to be replaced. There are 3 circuits in. Start, temp, and alternator. If the alternator signal is not coming in, you usually wouldn't even get charging on the truck. Now you can have a bad temp sensor and still get a normal reading on the dash for they are 2 different sensors. One is the sender unit sensor and the other is the coolant temp sensor for the engine. So I would start there first if the fuses are good to keep you from chasing ghosts all over the whole engine.
Again, I apologize for the delay for the site was down and I couldn't pull anything today after I got your VIN info.
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