Does any one know if a 92 f150 injector harness will fit an 89 mustang?

No, a 1992 F-150 injector harness will almost certainly not fit a 1989 Mustang. The engine bay configurations, engine types (likely a V8 in the truck vs. a V6 or V8 in the Mustang), and injector connector styles are all different enough to make this incompatible. Even if the number of injectors matched, the wiring and connector types would be different.