I have just bought one of these, do they need to be hooked up to a relay
Not sure what current they take but highly recommended to use relay operated seperate fused feed, since the fuse feeding standard horn is only 7.5 amps, and not sure of current rating of horn switch.
This is how I wired my Nautilus Horn:
Removed original horn and extended wires to drive relay coil. Took main power feed from redundant intercom connection (purple/white wire) which was shortest run from fuse box. Fuse 18 (power socket/intercom) uprated from 15 to 20 amp as horn takes 17 amps. 
