I was driving home the other day, and all at once I seemed to lose a lot of power... on the dash, the brake light came on (yet I have no brake problems), the tach and fuel guage turned off, as did the radio.
Seems to have pretty crappy power/acceleration to boot.
Battery is good, swapped w/ a new Orbital.
Thoughts?
Soudsn to me like a ground problem, but I don't have a clue where to start.

Check all the ground points, FSM shows the locations. Don't just look at them and say they look OK. Actually remove the grounding bolt, clean and wire brush the ground wire terminals and the bare steel where the bolt attaches and reassemble.

Well, I'm an idiot, hadn't checkled the most obvious thing...
Pulled the neg line on the battery while it was running - it died.
Guess the alternator is culprit #1...

Umm, that has been a bad thing to do for 20 years now (at least) Never disconnect your battery with the engine running. While you may get away with it, it can also destroy parts that were working fine until you did that.

Since most of your symtoms seemed to be dashboard related, I'd check the dash ground.

Dave

Had a similar problem just happen to me today. I was driving along and the tach and other guages died, as did the engine. Checked the fuses under the hood, and the 30 amp large type fuse was blown. $75 to tow it home. At least its covered by the insurance. To upset right now to dig into it. I'll get to it tomorrow. Probably a bad wire somewhere.

Well, mine turned out to be quite simple - 15A fuse under the kick panel.

What clued me in was teh fact that the guages didn't light up, but the CHARGE did, when I put the ignition to ON...
It also affected the gearbox, when in Drivem, it acted like it was fourth gear. Reverse pulled normally. I can only assume the auto tranny ECU is getting a ground off of the same line... odd.

I'm still perplexed as to why this also caused it to die when the neg battery was disconnected. FWIW I know is is not a good thing to do, but unf it's also a great diagnostic tool! i'd never add a load or drive it like that.

The same situation happened to me about a year ago. I thought it was my subwoofer overpowering the battery/alternator and got rid of the sub and replaced factory alternator w/ high output.

Then a few months ago, a guy from a shop drove it up to the lift and said everything just died and at first he thought it was really wierd. then he jiggled the battery ground wire bolted to the body and it was loose. Even though it was bolted on and you would think it's on good, just a little play makes a diff. The guy told me to bolt the ground to both the body and the engine block and no problem since.