Steve, You are incorporating a relay to actually supply the horn power I presume?? They do take quite a large current. My memory is a bit hazy but 40 years ago on my 3, I seem to remember that I ran a seperate supply line to the relay contacts and thence to the horns and used the [fused ] connections discussed above to drive the relay coil only. I dont remember fusing that seperate line [but if I did I would be putting in at least a 30 Amp anti-surge ] as its only temporarily powered unless of course you love the sound of windtones!! Hope this helps, Regards, - - - - - steve
To a man equipped with only a hammer, most problems look like nails