Electrical question for M1010 with Plan B Mod

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I am trying to understand the electrical system on my M1010. If there are folks out there familiar with this system, I'd appreciate some guidance. I'm an MV newbie. I worked as a Master Electrician in the theater, so I have a clue about circuitry, but little automotive expertise.

I am trying to keep the truck stock, to the extent possible, and to make it as reliable as possible.

The top alternator died, so we're doing the Plan B Mod, replacing it with a single-wire 12v alternator feeding the 12v distribution block, and disconnecting the DUVAC. It appears someone hacked up the electrical system before the truck was surplussed. We're trying to restore it to as near to stock as we can, given the Plan B Mod.

Recovery without the top alternator gave me ample experience at jump-starting the truck when parts of the system are not working. It also got me thinking about exactly how much of the system needs to be working for the truck to start.

Here is my question: Once the truck is working properly, is there anything in the starting circuitry that requires 12v at the 12v distribution block? I've studied the TM wiring diagrams, and I think the answer is "no", but I figured I should ask. I'm told the glow plug circuitry is 12v, but it seems they're fed from the 24v distribution block, through a resistor that evidently drops the voltage to 12v. The starter is certainly 24v.

I know things like lights, fans and gauges require 12v at the 12v block. If I understand correctly, I should be able to start the truck even if I have 0 volts at the 12v distribution block. I just need good power at the 24v distribution block. Is this the case?

I'd experiment, but the truck is torn apart at the moment awaiting parts, including the new top alternator.

 

[NDT]

You for sure need 12 volts. The injector pump solenoid, glow plug controller, and the starter relay near the ash tray are all 12v and needed to run.

 

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Thanks. When I recovered without a top alternator, the front battery was pretty much flat. I guess I must have been getting enough voltage from the 24v alternator to feed these. I'm going back to studying the wiring diagrams in the TMs.

You for sure need 12 volts. The injector pump solenoid, glow plug controller, and the starter relay near the ash tray are all 12v and needed to run.

 

[Recovry4x4]

Once started, you do need 12v to hold open the shutoff solenoid. I do understand that this isn't part of the starting circuit. I now wonder if thenflat battery is what cooked the upper alternator.

 

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It seems this truck has had a troubled electrical system for a long time. Someone in the military tried to fix it using an approach that is not in the TMs. It's impossible to tell whether their "fixes" fried the alternator, or whether they were trying to work around the alternator problem. I suspect the former.

The good news is the truck only had 1,911 miles on it when I bought it, presumably because the electrical system didn't work. If the Plan B mod cures the problems, I'm hoping for a long and happy life for the truck.

 

[Recovry4x4]

When chevyc60 did my truck he all but bypassed the troubled truck harness. He put 2 of the common Leece Neville alternators on the truck. Since they are an isolated ground design, each one charges a battery. The batteries in series provides voltage. They are running right at 28V on the 24V buss. The system is so simple and so effective, I'm converting another truck to this charging system.