Couldn't find an "edit" button today so will add the final (hopefully?) chapter to my charging problem as a quote entry.
Found that in the truck's prior life, all the wires from the alternator had been cut, then spliced and wrapped again. Not only the 2 large wires, also all the others. I finally got a good splice on the one large one that was loose, and then opened all the others to find a couple more bad splices in the smaller wires. After repairing them, the voltage check is as follows: Everything off, 12.5v at the battery terminals. Idling at 650, 14v. Fast idle, a little over 14v.
I believe this may have fixed the problem, but will keep an eye on it for quite awhile to make sure the battery is not being slowly drained, or that the alternator is not being damaged from overcharging. The in-dash volmeter never did go over the white zone when it was in it's prior "sometimes" charging mood (when one of the bad splices happened to vibrate into continuity), but I've never had any of my Fords show overcharge (higher than the middle of the in-dash meter) when the battery is fully charged. Today the in-dash meter shows about the same as the analog multimeter, however it's difficult to say because the in-dash one has only white marks(which seem to go to 14v) until you get to the red zone (which seem to start at 16v then redline at 18v), and the needle is now in the upper white zone which would be about 12v if the meter is actually working properly. Still makes me nervous to not see the needle drop down to the center, with a fully charged battery. As more work progresses on this I'll make sure all the groundings are good, as per the info in above posts. Could be all sorts of bad connections, after all it was a farm truck hauling everything from horses to fence posts before I got it.
Anyway, I hope this takes care of the charging problem; bad splices in a prior life on wires that were cut, for some absolutely unknown reason. Maybe it got so hot on the farm that the connector plug melted into the alternator so they had to cut the wires to splice in fresh connectors for the alternator. There has definitely been some heat on the smaller wires; enough to harden the rubber insulation.

 

That trick is useless on almost any vehicle with fuel injection. Almost any EFI vehicle will light a test light because there is enough static load on the system to power it. It is not uncommon for a newer vehicle to draw nearly .5A at rest. From the mid 80s to late 90s it should be less than .2A. The newer the vehicle the more load it will have just sitting in the garage.

 

Interesting. And one more reason to stick with my trusted '83.

 

Absolutely. The fewer tricky voodoo magic boxes you have the better off you are.