In my experience the fusible link either works or its blown. If the car is completely dead, that's the first place to look, assuming you haven't altered the wiring from factory. It seems you have a short to ground on the "alternator side" of the fusible link, otherwise I think the fusible link would have burnt up. I'd unplug the connectors at the bulkhead and then plug em in one at a time and see if the short comes back. You've at least narrowed it down some that way