OK! Looks like I finally have this resolved. Connecting a jumper cable between the alternator bracket and the battery negative made some of the accessories come alive (although not all of them, and not completely -- the radio would now turn on but produced no sound, for example). I removed and cleaned the heavy ground connection to the bracket and now had the same level of activity as with the jumper cable. But still no charging.
Checked the fusible links with a meter, and discovered that the 150A was blown. I replaced it, and everything is back to normal now! I'm sure I checked it before but might have overlooked it, since these symptoms are very different from those that showed up last time that fuse blew. The electronics on these trucks sure are weird...

 

Glad ya fixed it!

 

That's great! Glad to see you got it fixed.

 

Yeah, that's a tricky one. Nice work.