Fuel rail pressure sensor?

Hello, a high output or voltage high code for a sensor usually means there is a bad ground for the sensor, the grey/red wire is the Ground wire, its marked as SigRtn, I'll post a wiring diagram for you, I'm assuming you're reading 5-volts on all 3 wires? The ground wire does go to a Splice, Unplug the sensor and use the grey/red wire as your ground with a multimeter and check for voltage on the brown/white wire, that's the reference power feed. If you get no reading the sensor has a bad ground and the grey/red wire is open circuit somewhere. That sensor and the Power Steering Pressure sensor share a Ground at Splice S135 which I'll try to locate for you. Just don't jam the meter leads into the sensor connector, just touch the pins with the meter leads, and I will get the wiring diagrams for you.
What code is it setting exactly?

Here is the Ford OEM wiring diagram for the Fuel Rail/Temperature Sensor (diagram 1), with its connector pinout 2nd diagram and the location of Splice S135. So if you are missing Ground on the grey/red wire, you'll have to follow that wire along the harness, since no other sensors are setting codes, then either that sensor has an issue with its Ground, if the ground is ok, then its possible that the Feed voltage wire is shorted to the signal wire somewhere causing the signal to remain high all the time, The Feed (reference voltage should be 5-volts)
If you can't find any area where there may be wires shorted or melted together, you can unplug the PCM connector and check for continuity between pins on the Pressure sensor and that will tell you if they are shorted together, that takes the PCM and voltage out of the picture and just shows which wires might be touching with no insulation on them.
Look for locations where the harness has a contact point with the engine block, such as a bracket where the harness might be bolted to, those are the locations where the harness could rub through and cause shorts like this.

The PCM connector for the Fuel Rail/Temp Sensor is C175E, so it will be on either side since the center connector is C175B,
Diagrams 2, 3 are the pinout for PCM C175E if you need to unplug the connector, make sure the key is off first, but I would just start by following the harness from the sensor.

And that's with the sensor unplugged I assume? So that's correct, 5volt Reference is what you're reading there. What are you reading on the orange/green wire using the same ground but with the sensor unplugged? The orange/green wire is the Pressure sensor signal wire going back to the PCM.

What's the code number you're getting? Is it P0139?

Did you get things figured out?

These are the wire colors for the Rail Pressure sensor, are you testing these wires with the sensor unplugged or are you back probing the connector while it's still plugged into the sensor? The blue/white wire is the Fuel Rail Temperature sensor wire being at 4.97volts is fine that's not what is setting the code. I don't see any wire that's Green/White in color. At least nothing that has to do with the Rail Pressure sensor.

You need to unplug the PCM connector, leave the key Off, and check the resistance of the across the orange/green wire (Signal wire) and the brown/white wire (5-volt feed) at the sensor's plug.
Thats the Power feed wire and the Signal wire, with the PCM connector unplugged there should be no connection (continuity) between those two wires.

Next check the resistance from the blue/white wire (Temp Sensor) and the Orange/Green wire (Signal wire) with the Rail sensor unplugged and the PCM still unplugged. There should be no connection (continuity) between those two wires.

The reason you need to unplug the PCM connector is that the PCM sends out 5volts on the Signal wire to the sensor, When the sensor is plugged in, that 5 volts will drop to the amount of pressure the sensor is reading. It's called a Pull Up circuit. Thats why it's reading 5volts unplugged at the sensor.

The PCM will set a Voltage High code when it is seeing voltage close to 5-volts when it should not be, you need to recheck your Ground wire, put your black meter lead on Battery Negative and recheck your voltage readings on those 3 wires at the sensor, you're missing something here. If you don't get any voltage reading using the Battery negative
Check the PCM connectors for corrosion as well.

What are the exact code numbers you are getting? And is the PCM currently setting the codes or are they Historic (old) codes?