The ground busses that some have had problems with are located along both the left and right sills taped to the wire loom. There'* also a chassis ground in the right kick panel area. From the descriptions, I would not suspect corroded ground busses but it doesn't take long to check anyway. Here'* a pic of one in my 90. Yours will be in the same general area and on both sides:
I would approach this as if it were a parasitic drain. If you start the car and let it idle, it sounds like the headlights will be dim and the volt gauge will show lower than expected. At this point, start pulling fuses for non engine related circuits one at a time. If the lights become bright and/or the volt gauge seems normal start digging into that circuit deeper. Use this testing after you have ruled out the batt and alternator.