I recently installed a Stebel horn on my 650K4 despite a complete absence of relevant prior knowledge or experience, hand-eye coordination, or even adequate personal hygiene. It took me quite a while to parse through all the advice offered on various parts of the Intertubes (some of which was conflicting, inconsistent or unclear). After much prep, the installation went extremely well and the horn works perfectly.
I’ve put together this detailed guide in the hope that others might find it useful and be inspired to embark on such a project with less trepidation than I experienced. I’m hugely indebted to all on this forum and others who have posted their own guides and advice, and I hope that what follows helps to advance the current state of the art in Stebel Nautilusology.
The key factors to consider are: mounting the compressor as vertically as possible (the manufacturer asserts this is necessary for long life); protection from the elements; and ease of access for future maintenance. I considered 4 possible mounting locations for the horn, and 2 locations for the electrical relay. Here are the pros and cons of each option in my view.
1. Engine guard.
Pros: Easy to mount using hose clamps; easy to access in future; unimpeded sound on the left side if mounted on that side. Cons: exposed to water, dirt, stones and minor impacts; mass of the engine attenuates the sound on the side opposite the horn; difficult to mount the horn vertically
2. Vacant bolt hole in left side of engine block.
My Givi engine guards are too close to the engine to allow the horn to fit between them. Even if it did fit, the horn would still be exposed to rain and dirt.
3. Left cowling sub-frame.
Pros: well protected by the cowling from rain, dirt and minor impacts. Cons: On my 650K4, this is a very cramped space because of a forward extension of the fuel tank on this side and the ECU hanging down from the instrument cluster; also rain will fall directly onto the horn whenever the bike’s on its sidestand.
4. Right cowling sub-frame.
Pros: best protection from rain, dirt, stones and minor impacts; ample available space to fit the horn into; enables a perfectly vertical horn mount on both axes, which according to the manufacturer will maximize the horn’s lifespan and reliability. Cons: none, as long as the horn is mounted securely enough to prevent it from slowly rotating inward toward the forks.
1. Forward near the radiator hood.
Pros: The existing horn control wires can readily be disconnected from the OEM horn and connected directly to the relay without adding wiring between the two. Cons: The notoriously fragile relay is exposed to an undesirable combination of water and dirt; new wires still need to be run back from the relay to the battery.
2. In the battery compartment under the seat.
Pros: Easy to mount and access; perfectly protected from the elements; makes good use of readily available space. Cons: None.
I chose option 4 for the horn and option 2 for the relay.
As a complete noob to such work, my biggest obstacle was to find or create a wiring diagram that clearly spelled everything out in an idiot-proof manner. I got a lot of help from a variety of sources, but still found myself having to guess or experiment to some degree as I went along. The experience prompted me to create the attached diagram that I hope will help anyone else who might be as painfully dense as me.
Step 1: Mount horn
To minimize the chance of the horn rotating into the area within which the forks move while turning the handlebars, I decided to use a grounding clamp because it has very aggressive teeth and four points of contact to grip the bike’s sub-frame.
In order to also minimize the moment arm that tries to rotate the bracket on the grounding clamp, I made a small L—shaped bracket using a short piece of 1/8” aluminum flat stock from the hardware store. I bent this 90 degrees using some locking pliers, then drilled two holes into it using a hand drill and C-clamps, then filed all the edges smooth.
I wound some electrical tape around the sub-frame to protect it from the grounding clamp’s teeth. Over that I fastened the grounding clamp, to which I then attached the L-bracket, and then the horn onto that bracket. Wherever possible, I used locking washers with external teeth to enhance the system’s rotational stability on all axes.
I protected the system from moisture-induced short circuits and corrosion by sealing the connectors with silicone, which I also used to seal to all seams and any unnecessary openings in the horn’s compressor section (the heavy metal part of the horn). This abundance of caution later proved useful during heavy downpours in which the horn got wet but worked just fine.