Starter problems on an 84 Bronco II?

a fusible link works the same way that a fuse does, when it gets too much current through it, it over heats and brakes the circuit. i think that in your situation, you have a problem with the ring gear. that is the flex-plate between the torque converter and the engine or the fly wheel and trans if so equipped. if you hear the starter spin and the engine does not crank, then try to turn the engine over with a wrench in the crank bolt. it should not take much to tell if you can turn it or not. if it does crank, then double check the cables them selves to the relay and to the starter, along with the ground wire.