This is how the horns are installed in my Volkswagen Passat.
Three horns behind the grille, one were the foglight is supposed to be.
1/2 inch solenoid, relay and fuses in the engine compartment.
Then i bought a cheap garage compressor, kept the five gallon air tank, pressure gauge and pressure switch, and mounted a ViAir compressor on it.
Quick fittings so that it’s easy to remove when i need all trunk space.
Since the pictures were taken, air outlet is moved from the narrow pressure switch/gauge. Now i run huge 3/4 inch fittings directly from the tank.