I just recently upgraded my wimpy sounding horn.
You want to make sure that its attached to the mounting bracket. I made the mistake and only plugged the new horn into the existing horn one wire connection and tried to see if it worked, and it didnt because the mounting bracket is the negative aspect of the wire connection.
After researching this issue, I found the solution. I relocated the new horn and added a low toned horn by attaching and extending the positive and negative wire aspects with two 16 gauge wires, 2 female and 2 male quick connects. On my last car, the horn location was right inside the middle of the grill. After looking around for a few minutes I found the prefect mounting area just behind the grill. The new set of horns sound great now.