400A Alternator No charge vs overcharge??? Advice appreciated!

[HookEm]

I recently acquired a 2013 M1152 from GovPlanet and got it running and driving again, however it has a 400A alternator with a no charge situation. Voltage across the batteries is reading 24.5v (each battery is at 12.3v with engine off) while engine is running or not, volt meter gauge is showing steady in the yellow range. I am seeing 24.8v at the alternator.

Interestingly, I have access to another alternator and external voltage regulator, (I'm hoping not to have to swap the alternator as it looks to be 1/2 the weight of the HMMWV)... When I swap the voltage regulator however (no idea if the alternate is a good unit by the way) the charging system shows in the far red zone, voltage across batteries is 33v, so I promptly shut the system down and swapped the original voltage regulator back on.

I've checked the terminals at the batteries, everything is tight there, though I am using cheaper, non-OEM AGM batteries. I've tried to chase down all connections and confirm grounds, not seeing any frayed wires, but electronics is my weak point (this certainly makes me feel that way).

I'm trying to avoid buying another voltage regulator without confirming that's the issue as they're currently unobtanium.

I was thinking next steps would be to test the PCB? Any thoughts/advice would be greatly appreciated. I couldn't find any specific trouble shooting guides for the specific voltage regulator this unit has, nor anything specific in the public TM's for the 400A alternator.

 

[Mogman]

That does not sound like a PCB issue, all it does is excite the alt, that would be wire #5 attached to the sense terminal of the alt, as long as you are getting 24V there when the run switch is on then that is good.
At first glance I would say you may have two bad regulators that have failed in opposite directions.
I know it is a big expense but one of the most respected people on this site that refurbs HMMWVs, Retiredwarhorses would tell you to git RID of the 400A alt, so if it were me I would not spend any more on the 400A.

Edit I have no personal experience with the 400A so I deferred to someone that has experience and respect that has said in the past they are bad JUJU.

 

[HookEm]

That does not sound like a PCB issue, all it does is excite the alt, that would be wire #5 attached to the sense terminal of the alt, as long as you are getting 24V there when the run switch is on then that is good.
At first glance I would say you may have two bad regulators that have failed in opposite directions.
I know it is a big expense but one of the most respected people on this site that refurbs HMMWVs, Retiredwarhorses would tell you to git RID of the 400A alt, so if it were me I would not spend any more on the 400A

Thanks for your help, definitely considering a swap to a more affordable/accessible 24v alternative. I'll double check the voltage on wire #5. Thanks again!

 

[HookEm]

Thanks for the advice Mogman! 800 bucks well spent. Ended up having two bad voltage regulators.