The check list said to "STOP and find out why". The reason is anti-theft (PATS) is preventing your car from starting. No further tests were necessary.
Until the theft light goes out, this car will NEVER start. Note, PATS can be disabled with a hand held tuner.
Have you swapped PCM or cluster? Are you positive the PCM is alive? Did you have any issues with the swap? Anything disconnected under the dash?
Are you POSITIVE that fuses F2.21, F2.34, F2.5, and F2.37 are good? Don't cut corners here. A blown fuse could easily cause this and you could be in for a world of electrical trouble shooting "hurt" for something simple.
Check out the following thread for information on how to access the cluster diagnostic. The cluster DTC's may provide clues about what's wrong. https://www.allfordmustangs.com/forum...stic-mode.html