I recently purchased a 1984 Chevy pickup with a 6.2 Diesel in it, for $500 while on home for leave from Afghanistan. After replacing the starter, alternator and both batteries; and all the wires running from the starter and alternator, the stupid thing still won't charge the batteries.
The alternator bench tests just fine, and as long as my wife keeps it on a trickle charger, it runs like a champ, up until the batteries die (from using the headlights, wipers, radio, etc).

I read a similar thread but it was on a cummins, so I was wondering if anyone had any questions. It is almost like the alternator is not getting the signal to start the charge.

I don't know. I'm stumped!

 

The rectangle plug, one has juice all the time, and the other (exciter wire) turns on with the key. Trace the wire, and find out where it's broke and where it runs into the dash. May have to run a new wire to the ignition side (injector pump for example).

 

I thought I traced both the wires from the back of the alternator. One goes to the ground and one to the battery? Maybe not. Unfortunately, I won't be able to check until July/August when I get back home from Afghanistan.
My wife is getting pretty good at working on the truck, but the weathers been nasty so, I'll have her trace the wires when the weather gets better.

Thanks again.