At least with the later 240 taillights, the one farthest from the license plate on the bottom is the one that is supposed to light up. I don't recall if the inside lower one lights up with the brake lights, or if it just stays lit as a taillight. THis is as I remember it, not having a car in front of me while I sit at the computer.

The upper/inner red light(s) are the rear fog lights, and in 1987, your car should still have one each, left and right. But they are wired together, so if you unplug the left hand one, the right side will not work either.

Confused yet? I just remember from having to screw around with the taillights a lot. Make sure the proper bulbs are in the right spots, then trace the wires.