Alternator wiring /oil pressure switch
 

We had to replace the Ball Joints on my daughters 1989 240 DL today ..and afterward the car acted like the battery was dieing ...we looked by the alternator and there was a small black wire that came up toward the alternator in the same basic wiring harness as the large Red wire and the smaller red wire ...but the black one isnt connected to the alternator ..or anywhere else .thought maybe the mechanic knocked it loose when he was working on it ..the large red one is connected to the alternator and the small red wire is also connected to it via a small blue wire ....but for some reason the car wont charge ..any ideas on where this small black wire might go ..? Also there is a wire that goes into I suppose what is the oil pressure switch very close to the alternator on the side of the engine ..and it isnt hooked up to anything either and now the oil light on the dash is on ...I need some help ...that light wasnt on before today either ..and this car had no charging issues before today ..so if you could please shoot some ideas my way i would appreciate it..I mean does that black wire coming up toward the alternator hook into the wire for the oil pressure switch? ..thanks