That's exactly what was done! The number two fix in the link, that is. That explains quite a bit. Except that almost all the fuses on the lower half weren't getting any power. But this explanation satisfies me. And, better yet, I'm going to have AC this Georgia summer.

For some reason, the mechanic that did the fix made some seriously ugly connections between all the wires, so things were shorting out. In particular, he'd used a weird screw-in connector between the ground and the new fuse holder, and the connection there was loose.

Thanks for the info!