650ed wrote: . . . Fiamm . . . If you use it in place of the stock horn I would still put it on a separate relay to ensure there was no overloading of the wiring or horn button switch. Ed
I concur.
As known, a relay enables using a larger-than-stock wire to provide voltage from the battery positive terminal to the horn, and sometimes may also be used to provide a heavier-than-stock ground wire from the horn to the horn button.
In more youthful days, I used dual Fiamm horns on a 1973 Z1 for several years as replacement for the stock horn without noticing any wire-overheating issue and without blowing the 20 amp fuse. I used the Fiamms in typical horn manner for producing relatively short blasts. At the time it simply didn't occur to me any need to test for stock wiring and/or fuse limitations, or by keeping the horn continuously blowing for a prolonged period.
The Fiamms were the closest to a semi truck horn that I could find at the time, and the loudest available without using the more ear-piercing air-horn style. And this may still be true today.
According to various reviews on Amazon, owners are still installing Fiamms without a relay, while using the stock wiring, and without blowing fuses.
All that said, using a relay does seem to be the safer and better practice when installing the higher amperage Fiamm horn(s). However, lack of a relay with Fiamms should not necessarily result in fuse-blowing or over-heated stock wiring when the horn button is pressed in typical short-blast horn-blowing fashion (not for prolonged continuous horn blasting -- who does that anyhow??).
Just my 2¢.
Good Fortune!