If you look at the fuel pump relay in the top center of the picture and follow the gray wire down, it joins with a tan/white wire that goes to the hot fuel module and then to the fuel pump. The gray wire also goes to the oil pressure sensor. The power wire for the pump will carry the most current and should be the largest wire in the circuit. I would guess the gray and the tan/white wires would fit that description.
I have to ask you, do you have a carburetor that you are using now instead of the TBI and is the pump the same one that was used for that? If so then you must know that the fuel pressure will be too great for the carb and you'll need a pressure regulator to reduce it.
Are you planning on using the same harness and computer with the priming feature as the stock 87 used.
