The Hella 003399803 Twin Supertone Horn Kit includes both horns, a relay and install instructions. (Wiring and connectors must be purchased separately.)
The HELLA 003399803 TWIN SUPERTONE HORN KIT can be wired into the factory horn circuit but the power supplied by the factory horn circuit will not be adequate to produce the cited 118 dB. In order for the HELLA 003399803 TWIN SUPERTONE HORN KIT to function properly it will need its own relayed circuit.
Please see the following video clip for a sound comparsion.