My Air Horn Installation Log

I wanted to install an air horn on my Classic 1500, but wasn't very impressed with the options out there. The horns and system didn't seem "solid" enough for my tastes. In addition I didn't care for where all the horns were expected to be mounted. I searched the internet and found Howard's Horns and decided they offered the quality I sought. The main reason I felt good about them is the ability to remove the back plate and clean the diaphragm, which is something you can't do on models like Rivco. Below is a history of the installation.

I purchased the Howard's Horns "Big Horn" system, which includes the compressor, relay and braided airline. You can see in the picture (above) where I mounted the horn. I had to bend the mounting stem into an L, and shave some of it off with a hack saw. After carefully marking where I wanted the horn to be, I had to remove the inner engine cover, and drill a hole through it to run a single small bolt to the support the L bracket. The bracket is then attached to a C clamp which holds the horn in place. Since the trumpet throat is tapered, I noticed it could slide within the C clamp. The air hose at the rear should actually prevent this but just to be safe I applied a thin layer of J.B. Weld on the backside of the C clamp across the trumpet throat (which you can't see).  I then replaced the engine cover with horn in place. Below is a picture of the horn mounted without the side cover.

My next task was mounting the compressor. I found the perfect place for the compressor was under the side cover where the tool kit is stored. You will need to remove the plastic back of the side cover to make some cuts in it for the air hose. I used large dikes to snip away a notch so the air hose can pass through. Then drill a hole in the bottom to pass a small nut/bolt which will hold the relay in place. I then replaced the plastic back and began affixing the compressor. You will need to remove the snap in tray that holds the tool pouch, but leave the velcro strip which you will use to hold the compressor on one end. There are slots in the back which you can pass a stay tie through to hold the other end of the compressor in place. Once that is done the compressor is firmly in place. Now add the relay and you're ready to begin wiring. There are 4 posts you must wire for the relay. Ground, V+ which is only hot when the ignition is on, V+ straight from the battery and the line from the horn button which will activate the relay. Begin by wiring the ground and V+ constant lines. Attach the wires to the relay using the instructions from Howard's Horns.

Below is a picture looking down on the battery (under the drivers saddle).  It is wise to slit the post covers to accommodate the lugs and the tie wrap them down. The next thing to do from the relay is run a V+ line to a source strong enough to carry the load and which is only hot when the ignition switch is on. At first I ran this line right to the battery which was a mistake for 2 reasons. 1st, it means the horn is always hot, but worse it means the relay is always charged and will therefore drain your battery. I found the prefect spot for this on the fuse block which is under the opposite side cover. Remove it and expose the fuse block.

The brown wire I am pointing at (below) is where you want to tie in. This will supply the relay with V+ only when the ignition switch is on. I simply stripped off some insulation from it, wrapped the feed line to it and taped it all back up. Snaking all these wires is no big deal, but be sure and tie wrap in as many places as you can and avoid having any of the wires touch the frame. You can follow most of the wiring harnesses to accomplish this. Also be sure to leave a little slack at any bend to insure freedom for the wire as the bikes suspension operates. The next task turned out to be the most difficult to do, installing a push button.  I didn't want to over ride my OEM horns, rather I wanted both available. I found the solution to this after much pondering. Another reason you can't use the stock system is because when you press the button, you are not sending V+ to the OEM horns but instead grounding them out. Because of this I found it impossible to utilize the stock button. There may be a way, but it eluded me. Everything I tried resulted in blown fuses or the blinker lights not working. Following is my solution.

I discovered there was enough room in the left C clamp (clutch side) switch housing to install a small Radio Shack n/o spst micro switch. Since this on the same side as the OEM button I now had the ability to honk with my thumb (OEM horns), index finger (air horns) or both at the same time. Talk about getting attention! This is perhaps the most tedious aspect of the project. You must drill a hole through the clamp at just the right location to accommodate the switch. Drilling through this clamp is very easy. However be sure to mark your spot carefully so that the switch will fit properly. Wiring for this part of the project can use smaller gauge wiring, but try to use 14 gauge if possible. DO NOT use solid wiring for any of this project, only stranded. Routing the wires from the micro switch back to the relay is a bit daunting. You will need to remove the screws holding the hi/low beam headlight switch and horn button. Because the wires must run from the front side of the switch housing, under the handlebars and then back down the handle bars, you have to route them so they follow the wires in place. It can be done, but just takes some patience and a steady hand.

One more picture of the micro switch

Below is a shot of the wires from the micro switch down the handle bar wiring harness. I was able to pass the wires through the same harness loom that comes out of the switch housing. From there I simply tie wrapped them down existing harnessing. My only regret was using green instead of black wiring (which was all I had). However I will at some point replace this so the green wires are not so obvious. *UPDATE* Replaced the green wire with black and hid all behind the wiring harness.  I terminated and wired together the following wires in the headlamp housing-2 wires from micro switch and the wire from the switched V+ (brown wire from fuse block) and energizer wire to relay. It's quite easy to feed these wires from switched V+ and energizer from relay to the headlamp under the gas tank going through existing tie wraps. The reason you want to do all this termination wiring in the headlamp is because it offers a point where the position of the handle bars does not cause a pull of the wiring wherever the front tire may point. After you get all this done you've pretty much got it licked. The only thing left is to clean up the install.

Below is another shot of the horn/compressor setup. As you can see from the photo I was able to pass all the wires for the compressor through an existing hole in the side covers plastic back plate. I would describe this projects difficulty as medium for those who are mechanically capable using a minimum of tools. You do need to solder the connections at the battery and micro switch, but all other connections were either crimped or simply wrapped together and tapped. The cool thing about this project is that the air horn does not hang out there off the front end of the bike which can interfere with those who have crash bars. It also does not require you to eliminate your OEM horns and it gives you the added safety of being able to honk with either a thumb, index finger OR BOTH. The placement of the air horn button is natural and within very easy reach. Below is another look at the compressor relay installation.

While the Howard's Horn system is not dual trumpet, it is LOUD! I bought my system for $100 through their scratch and dent sale. The imperfection can hardly be seen. The regular price is $150. Another thing I like about their horns are the use of braided air hose line. Many of the other horns only supply you with clear plastic hose. Without the restriction of braiding, theses hoses expand and do not deliver the air volume at rate needed to be loud. I close by saying I am in no way affiliated with this company. I was just very proud of the fact that I was able to do this very custom addition to my bike and wanted to share it with my fellow VROC members.