[LarsMac]

Specifically, I have a Class C RV on and 2000 E-450 Chassis.
Vortec V-10 motor.

I let the battery drain down to the point where it would not turn over.

I've taken the battery down to NAPA, recharged, and tested. It seem fine, passes load test, fluids are good, and fully charged.

Now engine turns over fine. Too fine. It just spins, never even a hint of a spark.
Back when I was a kid, this was a simple problem to troubleshoot.
Check the points, check carb. It is missing fuel, or it is missing spark. Put a finger on the plug wire and see if you get a zap. (Yeah I actually tried that a few years ago, and learned that it is now a REALLY bad idea. I still have the scar on my knuckles)

I live out in the boonies, and everything is a two to three hour drive, so calling in a mobile tech would be a last resort. Last time I actually worked on a vehicle was back in the seventies when the computerized stuff was just getting started.

is there a "simple" OBDII device that will give me a clue? Can I safely pull a plug at test for fire? How do I tell if the thing is getting fuel to the cylinder?

I did find the fuel shut-off switch and it does not seem to have engaged.
I also can run the generator, which feeds off the fuel tank, so I know that the gas is good.

Any useful advice will be appreciated.