6pak is right about the accessory circuits are probably not the problem.

If you insist on a fuse go to at least a 40 amp. I am currently running a 30amp in my /six No AC/Radio/Washer pump barracuda and it works OK but I don't drive at night when I would need headlights.

I lay odds the fusible link was just a victim of age, every spike weakens them and eventually the individual wires inside start to break one buy one until a catastrophic failure occurs. If it's an unmolested or improperly repaired harness I lay odds the problem lies in the harness itself. It is very common for the main power wire to slowly melt over time and short into other wires. Eventually it will find a ground through a circuit and the fusible link goes bye bye. I had one melt into the headlight switch wiring. I couldn't turn off my parking lights but I could dim them with the dash panel dimmer.

The wiring from the factory is minimal at best. I bet if you peel back the cover on the harness behind the fuse block you will find the black or red large gauge wires are melting.

Rebuilding a harness is pretty easy. Pull the whole dash and lay it on a bench. Pull the harness and unwrap it using plastic ties to keep the bundles loosely configured so it will be easier to re-wrap. Inspect the wires and if you find a bad one SOLDER a repair/replacement wire in it's place. Do not use crimp connections alone. Those are a bandaid that will eventually fail. Re-place the main power wires with a wire at least 1 gauge larger and don't use the factory bulkhead/harness connectors for the main power (ammeter/Alternator) and main ignition switch wiring.