Your car's horn makes a distinctive sound by design. So that other motorists can easily recognise your vehicle based on the sound of the horn, smaller cars are equipped with a higher-pitched horn than that of a larger vehicle. To make your horn louder, you have two options: adjust your horn or replace it altogether. Both tasks are relatively easy to perform.
Disconnect the grounding wire from the car battery. The grounding wire is the black wire connecting the battery to the frame of the vehicle.
Locate the car's horn. The usual locations for the horn are by the battery, under the hood near the front grille or above the left or right wheel wells.
Unscrew the screw securing the horn to the mounting bracket.
Inspect the horn for an adjusting dial. The dial will be on the side of the horn and require a flat screwdriver to turn up the volume. To turn up the volume, turn the dial clockwise until your desired volume has been reached. Reconnect the horn. If there is no dial, you will need to replace the horn with a louder horn.
Disconnect the power supply wire from the rear of the horn. Attach the wires to the new horn.
Reattach the new horn to the mounting bracket. If the new horn is the same size as the old horn, replace the horn at the same location. If the new horn is substantially larger, you may have to find a new location for mounting. Choosing a new location will mean detaching the entire horn mounting bracket (done by removing and replacing the screws).
Reconnect the grounding wire to the car's battery. Test the horn.