Answering Ponchogl's original questions "is this a fuseable link? Is it necessary ? Is this common and do I need it in the new wire. "
using John in Utah's wiring diagram ...
It doesn't look like a fusible link to me. Probably just a connector.
Necessary? No
New wire? I'd replace both wires.
The factory wiring did not have a fuse of any type for the horn circuit. If you'd like to install one, I'd place it as near to the ammeter as practical. That way it would protect as much of the wire as possible.
Fuse value? I don't know.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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