I cannot seem to find any of my older wiring diagrams. All I can find is 1990+. I believe in '89 the fuel pump relay and perhaps the PCM relay were under one of the seats. In 92 or so, Ford moved those relays to the engine compartment. Since the location changed, the wiring colors may be different.
Still, it should be pretty easy to figure out which wires are which.
They'll be four connections on the fuel pump relay. Two in, and two out.
1. [IN] Hot all times B+ (HAT) directly from a fuse link. Later models show it as Pk/Bk. This is the power that comes into the relay, is switched, and goes out to the fuel pump.
2 [IN] Switched power from the PCM relay. When the PCM relay is activated by the ignition switch, the PCM relay flows power to the fuel pump relay for switching purposes, not power to the pump. Late model color is R.
3. [Out] LB/O. This runs back to the PCM. It is used by the PCM to switch the fuel pump relay so that power (coming in from 1.) can flow to the pump.
4. [Out] This is the power output to the pump. On later models, it starts out DG/Y. After the inertia switch, its BR/PK. It goes through a connector, and is Pk/B on the fuel pump side.
The fuel pump circuit is grounded in the rear of the car.
If the color coding is different on your car, just take a look at the back of the relay. It's a standardized connection, and may even be labeled. Labeled in the sense that each connection will show a pictograph of what it does.
Just open up the connection under the hood, and do a few continuity checks. Should be pretty easy.
Here's a relay diagram,
And the two diagrams I explained above that show the fuel pump relay for later model Fox cars (93)
Just to clear about this, the circuit will be exactly like above. It just may have different colors and the relays may be in another place. Once you I.D. which wires are which at the fuel pump relay, just check for continuity at the connector in the engine compartment, and you'll have found the wires you want.