'82 200sx- car slowly dies after turning on headlights & other issues

Hey Gang-
just picked up an '82 200sx that has a few issues-
1) has some vacuum or MAF issues; hesitates a bit when revving it, falls on its face when accelerating, then picks back up like normal when you back off the gas & accelerate moderately.
2) more pressing is the issue that when you turn on the headlights, it will bog the engine & stall within 5-7 seconds, then return to "normal" if you turn the lights off
3) Also at night with the car off, when you step on the brake the parking lights all light up (front & back)

The alternator puts out 14.1 to 14.2v when running, even right up until it dies with lights on. I load tested the battery & it's within range @12.5v.
It would make the fan belt squeal when it was dying, so I tightened the fan belt & it doesn't squeal now.
I cleaned off / sanded down to bare metal & re-attached the neg. ground at the battery bos, & cleaned up a few more grounds I noticed.
Any ideas? This one has me flabbergasted. I suspect that's why the kid / PO sold it. Couldn't find anything on this issue via search.
Thanks