Military Vehicle Repair: 24 volt electrical: one battery not charging, field biologist, intermountain west

Question
I have a CUCV with a 24/12-volt system.  All of a sudden one of the batteries is not charging (the one closest to the firewall and the first one in series).  The second battery which is connected to ground and is daisy chained to the first battery via a negative-post-to-positive- post connection charges fine.  I am not a terribly experienced mechanic and I guess my question is: where should I start trouble shooting this issue.  Both alternators are producing juice at 14 volts each and both batteries are in good shape.  Also, do you know where I can get a wiring diagram for this system?
Any help would be greatly appreciated,
- John

PS - I am a field biologist in the intermountain west and this is a killer car for the backcountry with quite sweet mileage...runs on biodiesel as well...

Answer
In the dash, above the parking brake lever, is the light for alt 2 on?
If not, the bulb could be burnt out. it provides the excitation for that alternator. Goes to the small plug on the alternator.

Also, check the fuses under the dash for a loose or blown one.

memphisequipment.com should be able to come up with a manual.

Van