Ford F-150 (2004-2008) :: 2005 FX4 Died Suddenly - 4x4 And Audio Don't Work

Last week, my 2005 FX4 Screw died suddenly, and would immediately lose all power to the gauges as soon as the jump leads were disconnected, not to mention the engine would eventually die shortly after that. After a bit of logical thinking, a buddy and I determined that it was likely the alternator, so we pulled it and replaced it. We also had the alternator tested, and it failed every single test, so it was pretty clearly the culprit. The good news is that the truck starts and runs/stays running again. The bad news is that my audio and 4x4 systems are both offline.

As far as audio goes, I'm guessing it's an easy fix because it's probably a fuse somewhere that got toasted. But the 4x4 is a little more of a problem. I tested the vacuum lines by pulling them from the hubs, and neither had any suction. Okay, the solenoid isn't getting power, probably another fried fuse, right? Well, here's where I'm getting confused.

My understanding of this 4wd system is that it works like this: When in 2wd, the solenoid engages the vacuum and pulls the part of the hub that locks in the wheels (not sure what specifically to call it) out, therefore disengaging the front 2 wheels. When 4wd is turned on, the vacuum disengages and that part of the hub pops into place, locking out the front wheels into 4wd.

So, by that rationale, if the 4wd solenoid isn't working due to an electrical issue, then my truck should automatically just be locking itself into 4wd, right? Because without the vacuum to disengage that part of the hub, it should just pop into place and keep the truck locked into 4wd. So if I'm correct in my understanding, then I have another problem because my truck is still operating very much in 2wd.

I did the classic 4wd tests: tight circle to feel the front end gripping/pulling, gun it from a dead stop to see if all 4 tires engaged. But I turned in a much tighter circle than 4wd would ever allow, didn't feel the front end grip/pull at all, and the "peel out" test only showed my 2 rear tires as launching me forward. I also tried shifting into 4-Low, but the truck never shifted into low gear either. -I know that's probably just electrical, but I'm just trying to be thorough in my testing/explanation.