I have an 87, no air and manual transimission, but I will go see if I have a wire like that. I would guess it to go to one of the intake manifold bolts, most likely the same one your glow plug controller hooks to, but I look at mine.
On edit - Mine does have it, it goes down and hooks to one of the upper bell housing bolts. Has anyone had the transmission out of your truck? I would guess they forgot to hook it up. I would also not hesitate to hook it to the stud on the intake that also has the solid state gp controller hooked to it. I would also run another ground from the frame over to the motor as well. I ran one on each side front to the frame, then on the d-side, I ran a 10 ga wire up to the stud on the intake that I have mentioned. These trucks have terrible grounds and anything you can do will help. You may find that some of your wiper problems are ground related but you stated inoperative pump, which generally is a failed pump. I would check for volatage at the pump with someone holding the button in, if you have power, you need a new pump, if not, you may have a bad switch or possibly ground problems.
Good luck!