If the PO ditched the FL, perhaps there was a reason he did so - maybe it was getting fried due to some other problem that may still exist.

Anyhoo, FL generally is, IIRC, 2 gauge sizes smaller than the wire it serves to protect. If the FL was on a 10 gauge wire, FL should be 14 gauge, I believe. You can make one pretty cheap. THe FL wires are available as kits in any electrical supply section of the auto parts store. Easier - and cheaper - than buying a whole repop harness. Although, if your whole harness is hacked up, a new one might be more accurate and/or less prone to overheating/frying your car.