Ford Repair: Ford F150 Electrical Problem, fuel pump relay, wire sensor

Question
Dennis,
I have a 1987 Ford F150 with a 5.0.  I have not been able to get it started because the fuel pump will not operate. I have traced it down to the ground wire on the  fuel pump relay. This ground goes directly into the computer. I have replaced the computer and still no luck. It looks like the computer controls the ground, but I have no internal schematic to see what might be making the computer not work. If you have any suggestions, I would be glad to hear them.

Thanks,
Dave

Answer
You are correct in that the ground goes into the PCM. Ford uses ground control for a lot of the electrical items on their vehicles.

For you I would suggest you check all the grounds you can find, on the fenders, near the battery; I think there may be one somewhere on the engine, in 1987 maybe at the back of the heads, possibly an orange wire. It's been a while since I have worked on one this old, and I don't have manuals that old here.

Have you checked the power from the PCM? Find a red wire, on the idle control valve is a good place. Check for battery voltage on that circuit with the key on. You might also check for reference voltage at one of the sensors, brown or brown/white wire, usually the center of a three wire sensor, see if you have about 5 volts there. Then we will know if the PCM is working.

Let me know the results of these checks and we'll go from there.

UPDATE: I was reviewing the answers that I sent out today, and I may have been incorrect about the wire color for the reference voltage that I mentioned. Some part of my brain tells me in the late nineties that circuit was black with a white stripe. I hope this doesn't confuse you any more.
You can be sure it's safe to check each of the three wires on a sensor for that 5 volt signal, as long as the sensor is disconnected, one of them should show 5V with the key ON.