Just wondering. Have you confirmed the PCM ground? As a reminder there is a separate ground wire that goes back to battery negative. Recommend using a test light that will "load" the circuit. This will confirm the circuit's ability to carry real current.
Also, has key on power in and out of fuses F2.34, F2,2, and F2.8 been confirmed? Again using a test light that will load the circuit.
Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/
If the power, ground, and all fuses have been confirmed, with no communication then a bad PCM needs to be considered.
Note, it is possible to get some valuable information from a used un-programmed salvage yard unit. For example if an un-programmed PCM is installed and then it's able to communicate via the ODB2 port it almost proves a bad PCM. Try car-part.com for some sample used units.
Here's some more information that my help.
ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/