Zeke,

I don't believe (You) (or anyone else reading this) has understood the significance of your sentence:
"The wires coming to the 3 port junction just behind the expansion coolant tank all look good - I had previously cut out the burned ends and spliced new terminals on."

HOW DID THE ENDS GET BURNED?
(Just cutting off the SCORCHED ends of the cable does not "FIX" the CAUSE)

Did this chassis suffer a FIRE?
[It MAY in the Near Future,with the symptoms you describe]

Find the CAUSE of the Power Transmission Cables BURNING and then you can
confidently fix the problem.

Unsolicited Rant:
If I've got Alternators "Going South"
(I don't know what else to call it,'Cause you can't tell us How,or What FAILED in the Generation System.)
AND I'm seeing Burned Power Transmission Cables...
I'm not risking Myself or the Chassis by operating the Vehicle.
UNTIL the Anomaly is COMPLETELY diagnosed and rectified!

__________________
'84 300SD sold
124.128