If you’re trying to check the fuel shutoff solenoid you need to bump the starter to see if it is working. One wire is ground, one is to pull it up (when started is engaged), one is to hold it up. If it doesn’t pull up on its own, leave the key on and pull it up by hand. It will probably stay there. If not, just take it off. If it’s getting fuel and has compression it will run.
By the way before you start chasing it, there is no throttle body and diesels don’t have vacuum. It doesn’t care about any sensors.
Also, if it has coolant in the oil but no oil in the coolant, that means your leak is where coolant pressure is higher than oil pressure. So you can rule out the oil cooler.
When testing it was not moving, I did try to physically press the solenoid plunger up and it wouldn't stay.
Now everything makes sense;
although I think I'm missing a spring so the fuel shutoff lever returns to the run position (ccw down)?
Sounds like this is a known issue on the forum, good link
here. Weak batteries can cause a retraction issue if the voltage is too low.
A PDF on the wiring lifted from the other post is attached. Cummings part #: 3921980
Black = Ground
White = Pull-in
Red = Hold-in
As far as the leak, I can't be 100% certain there was no oil in the antifreeze if so not much; I was hoping it's the oil cooler..
I've not tracked down this critter yet circled in
red, but I'm assuming it's a check valve or filter? part # 21415
In the
yellow box black seal easily falls off, is this a dust cover?
Also in the yellow box below it looks like another uncapped connector?
I'll be at in again later in the week; here's a picture of the truck: