Did you actually read what the OP posted - perhaps not.
Last time I looked the OP wanted advice on fitting a FIAMM Mini Blaster which supposedly takes just over 5amps which is why it is marginal running off the CANBUS
I was quoting your post to address the question of why the OP might find a power distribution system of some kind useful, as it would be suitable for powering HIS horn. It is totally irrelevant what you connected to yours and how much current it takes, though if it is really 18amps then it must be an incredibly inefficient design.