You can get away with just switching out the stock OEM horn for the FIAMM low tone and not need to add a relay. Having both the low and high tone with draw too much amperage for the switch. The FIAMM set on a 12 volt power supply draw 4.5 amps for the high tone and 5.5 amps for the low tone. You might want to use a relay. You can make your own or buy one pre-made.Motorcycle Horn Relay Kit, cheap Worldwide Shipping You may not even be able to hear the stock OEM horn over the other two.