I guess I need a good schematic. I see the one from a post earlier, but I'm not 100% sure I'm reading it right.

Orange wire is the one I disconnected, and use my manual ground button. The red wire has power at the relay.

Yes, I did remove the wires to test. The red has power when cold, but the orange does not. In fact, it doesn't even have continuity to ground when cold.

I know typically the pcm will trigger grounds. I just don't know here. It's weird that the pcm would command a ground for the GPR, then command 12v for the GPR to shut off. But I am not all knowing, that's why I'm here!!

i kinda thought that the pcm sent power to send the juice and the ground was not controlled.

I don't usually have to troubleshoot pcm problems on my Fords, only the Chevy trucks. I had an issue of injectors, and the pcm wasn't pulsing the ground for 1 cylinder. That's what I'm falling back on. I just thought that pcm's pulse grounds...but as I said before... I'm not all knowing...:c:

wiring is not my thing to be honest. but didn't you say there is no continuity between the relay end of the wire to the 42 pin connector?

I didn't check it yet. I need to find that connector. I had 10 minutes to run my testing before I had to move on to the more important things :dang:

I'm really good with wiring, just not up to par on this one...yet...

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I meant that there was no continuity of the orange wire to ground when the GPR should have been commanded to be on.

PCM uses grounds for activation on the relays and varying voltage on regulors (IPR valve, EBP valve, exc). no continuity sounds like a bad wire/pin in connector. Id pull both the 42 pin connector and the main at the PCM and to a continuity test all the way from the PCM to the relay and I bet you find the problem. The 2 bad PCM's that Ive ran into on this both were sending hot and just never sending the ground signal so since no hot pressent on both Im guessing wiring.

The PCM uses POWER AND GROUNDS to control your circuits (5v to most sensors). In this case you have a bad ground that IS NOT PCM CONTROLLED. The PCM provides power to your GPR to switch it on and off. A PCM cannot "send a ground signal" (because a ground is just a ground, no voltage), but it can open up a path to ground (this is not your case).
I will re-post where this ground goes to

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I've traced the wire (it's red or violet with an orange tracer) back to the PCM, so the circuit can have a constant PCM ground (unswitched).

Like someone said up here already you're gonna have to test the wire from the GPR to the PCM connector.

Ok, that sounds good on both posts. I didn't have time to check it today, maybe tomorrow. Where is the 42 pin connector at?

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Scratch that, I found it. Thanks for the great info, will post when I get more into it.

Then why is one wire always hot (power thru PCM from one of the two ignition fuzes)?:nope: PCM sends ground to complete circuit. There is no constant ground and wiring a constant ground will fry all 8 glow plugs. IH does this on a lot of things. Become a certified Navistar dealer and you'll learn this fast. The ground is the signal and is PCM controlled. That wire is your problem or the PCM itself isnt activating.

the only constant power is the one big post on the GPR. the two smaller posts on the GPR are PCM CONTROLLED. THEY ONLY TURN ON WHEN THE IGNITION IS ON. your 2 fusable links coming off your starter solenoid are only for the high amp side of the GPR.

your glow plugs are grounded in the cylinder head, therefor they have a CONSTANT GROUND.

again. there is no such thing as a "ground signal". the PCM can only provide a path to ground. IN THIS CASE you have a CONSTANT ground provided by the PCM, which is the same ground that EVERY SENSOR on this engine grounds to.