I am now using the 30 amp.
In my case the body shop jammed the top mechanism and then rode the switch, this burned out the orange wire that goes from the fuse panel to the horn relay causing a small fire at the firewall.

Unless you owned and serviced your vehicle exclusively and have checked the engine bay wiring minutely most of the fusible links have long since fused and been bypassed/replaced with something by somebody, somewhere.

As far as depending on 40 year old fusible links, they are not what they used to be and finding and repairing old brittle wiring is not as much fun as some people think.

This was true on my 350 conv and my 400 coup. that wiring is OLD.