If you ever want or need to use the 90 amp output, 8 gauge would be preferable vs 10 gauge as many have suggested. You probably need to go to an auto electric store to get 12 gauge fusible link to go with it or use a "maxi fuse" from NAPA rated around 120 amps.

That said, a 10 gauge bypass would be a whole lot better than what you have now. You are fortunate the bulkhead connector hasn't melted yet. I melted one years ago with a 60 amp alternator.