lost all and complete power today while driving,now wont do ANYTHING,NOTHING.

husband checked battery and altinator,fine has full amps..but nothing at the fusebox..he put an insulated wire running from the battery terminal to the fuse box and it starts right up..could it be as simple as just that main wire linking the two?..and how to replace it(whats it called)...maybe a relay?..please help,and thank you very much!!

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