Will a 1991 5.0 Thunderbird motor-wiring bolt up to 1994 3.8 mustang?

No, a 1991 5.0L Thunderbird engine's wiring harness will not directly bolt up to a 1994 3.8L Mustang's engine bay. They are completely different engines with different computer systems, sensors, and wiring configurations. You would need a significant amount of custom fabrication and wiring work to make it work, and even then, it's a complex undertaking that requires considerable mechanical and electrical knowledge. It's not a simple swap.