The Differences Between Heavy Duty Train Horn Wiring and Standard Horn Wiring
First in a heavy duty setup the train horn will a pressure switch that will go specifically near the exhaust of the air compressor. The switch will have two separate wires that come from it. First there is the positive charged wire that will move directly to the battery or other material that creates the 12-volt energy needed for the horn to work properly. Second there is an individual wire that connects to a relay terminal.
The relay terminal that is used will have four wires coming from it. First there is the red wire on terminal 87 of the relay that moves directly to the air compressor. A blue wire is then used from terminal 86 to the pressure switch.