The only thing I would add, is to control the relay circuit by controlling the ground. Especially the horn. Feeding 12 volts positive up a steering column just wouldn't be prudent in my opinion. If that same wire were to short to ground - but control the ground side of the relay circuit, the horn would blow and alert you to the issue, if it was 12 volt positive and going to ground (shorted) you'll need to rely on the fuse to open and protect the circuit. So one day your horn is needed and it won't work. Or worse you've inserted a wrong sized fuse and the wire melts the insulation or worse.