In my 72 it is screwed to the firewall above the distributor. It has a post sticking straight out of it with many wires connected to the post and the wires connected to the underside of it which are...
horn relay location - Victor.
under the dashboard.... way up high behind the headlight switch, next to the seatbelt buzzer, you must access it by removing the lower duct hose and vent assemblies,...