Any BMW Club member who has ever attended a chapter or national event has no doubt heard many of the BMWs at the event “sound off” their air horns. You’ve probably wondered what’s involved in installing these, and how you might go about it. This article should help you.
Air horns consist of an electrically-activated compressor which forces compressed air through tubing to the horns themselves, which provide the sound. Ordinarily, horns are bought in sets of two or three trumpets. To make the air horns work, you must wire up the compressor so it is activated by some electrical switch; it, in turn, delivers the air to the horns.
The simplest way to accomplish this wiring is to use the “hot” lead to your factory-installed electric horns. Here is a recommended procedure.
First, determine where you are going to mount the trumpets. Depending upon the type of car you have, they can be mounted together or separately. Since the brackets supplied by manufacturers usually provide for mounting the two trumpets together, you may want to take a hacksaw and create two mounting brackets from the one provided by simply cutting the bracket in the middle.
On my BMW, I mounted the two trumpets separately without drilling any holes in the car. I simply removed the bolts holding on the existing electric horns, slipped the air horn mounting brackets under these bolts, bent them to fit the existing space, and re-tighten the bolts.
You must then determine where you are going to mount the compressor and make sure you have enough tubing to run from the compressor to the trumpets. If there is not enough in the package supplied by the horn manufacturer, you can supplement this with fuel line, which fits quite well (but check it first before buying it). The compressor must be mounted upright so you can get at the oiling hole. If possible, use existing bolts and holes to avoid having to drill new ones. On my car, I was able to use one of, the radiator mounting bolts and a pre-drilled hole in the sheet metal next to it to hold the other end of the compressor support.
Once you have connected the trumpets and the compressor, it’s time to start wiring. If you want, you can always wire a separate switch through a relay, and the horn kit ordinarily comes with such a relay and instructions for installing it. But there’s an easier way. Strip a bit of the wire leading to the hot lead of one of your electric horns. You can tell which is the hot lead because brown is always the ground on a BMW. Run a wire from this stripped section to the hot lead of your compressor, which will be marked “+.” Tape the wire carefully where you made the splice on the electric horn hot lead. Then, you will notice another lead on the bottom of the compressor, marked “,” which is for a ground wire. Run a wire from this terminal to a good chassis ground (remember, painted sheet metal does not ordinarily provide a good ground).
Now you have a system which will work off your existing horn button and does not require any additional wiring through the firewall or dashboard. When you hit your horn button lightly, you will get an electric horn sound. Lean on the horn button, and you will get both the electric and the air horns.
The effect is electrifying! Pokes who don’t respond to flashes of your headlights or polite toots of your electric horns always move over when you hit the air horns. They look like they wonder what hit them. Air horns can also be a definite safety device. My secretary tells me she was run into the center strip of a highway by a truck which simply didn’t see her. Had she been able to lean on her air horns, he probably would have stayed out of her way and her car would not have been damaged.
The whole procedure of installing air horns should take no more than an hour, and the results will be well worthwhile. Give it a try; you won’t be sorry and you are almost sure to be the only kid on the block with this type of automotive sophistication.
Author: Richard 0. Neville