Immobilized car, electrical problem

[Thunderscreech]

Greetings! I sold my 2003 Vibe to a friend and she's having a problem that I encountered a couple years ago and thought I'd fixed.

Here's the symptoms when it happens: The car can start, but very few circuits inside the cabin power on. The radio and dash is dead, the car will not shift out of Park, and the battery does not charge. The automatic headlights do not power on, but if you manually switch them on they do. Turn signals work.

Physical manifestation: In the fuse block under the hood, the ALT 100 fuse got so hot on ONE terminal that it melted the plastic. Since it didn't blow the fuse and only one terminal got hot (I actually saw it glow), I assume the problem was a poor connection at the terminal causing it to become a resistive heating element.

I re-seated a new fuse a while ago and everything started working fine, but a few days ago the same symptoms re-appeared and the circuit had gotten really hot again.

Because the fuse block was deformed, I pulled the fuse block and disconnected the burnt terminal. There's a fat white wire with heat damage and I trimmed it back an inch and mounted it to an inline 100AMP fuse then made a fat jumper wire to complete the circuit to the other side of the connector (the driver-side) which is a copper bus bar that runs through half of the fuse block. It has continuity and everything seems to run at 12v there as expected...

...but the inside symptoms persist. I've checked the AM1 fuse, ran through every fuse under the hood and dash with a multimeter, even swapped around a few same-rating ones in case one had failed in a way that passed continuity test. Nothing.

Can anyone suggest part of the circuit to investigate that could be interrupting power to the components I mentioned?