The Grover 1730 installation kit for vehicles with air brakes includes everything you need to get your air horn installed!
The Grover 1730 includes the following: 
Grover 1136 Solenoid Valve
Horn Button with mounting hardware
14’ wire
8’ tubing
1 x fitting: ⅛ NPT female (for valve)
Tube protector
2 x fittings: ⅛-27 NPT male with attached tube protector (one for valve, one for air horn)