Like many I don’t much like the standard V 85 TT horn and sought to replace it with a pair of Fiamm alikes. Easy enough to fit on the crash bars and power taken from the standard horn wires. Fine, all works - to start with. Then it goes intermittent and stops altogether. Ok, thinks I, perhaps I should have used a relay and the load had been too much for the switch. So a relay was fitted and still the horn was not good. Thinking that the switch was at fault I asked the dealer to check and they agreed that this was the case and would fit a new one. Come the day and the new switch does not work either. So the next step on returning home was to restore all to standard, and lo, normal service was restored.
Why did this happen? I’m not an auto electrician but can manage simple things and have fitted similar systems to several Can Bus BMWs successfully.
Ah, Can Bus, that beast from the depths of the warlock’s black arts.
As I understand it all the individual subsystems have a range of values to work from and the thinking is that if the system goes outside of these parameters then it throws a wobble.
In this case, going straight through the switch probably asked too much and caused the issue. So why did it not work with the relay? It’s only an educated guess but I think that the current draw was now too small and therefore fell outside of the parameters again but on the low side this time. Yes it might work with a resistor but that is outside of my experience/comfort zone.
With BMWs if you go outside the zone and a fault occurs it’s normally a case of switch the ignition off and on again to reset. In fact some BMs will take the twin horns on the switch and some won’t, it appears to be luck of the draw. They also don’t use fuses, dealing with faults electronically.
For the time being, therefore, it’s staying standard until I find a better alternative.
Blimey. Thanks for sharing your experience. I was tempted to do something similar, not being impressed with the “meep meep” sound of the factory item. Now I know to avoid that trap.
First of all I would want to esablish whether the horn does indeed involve the canbus. I can’t see why, it’s so simple. But who knows? But certainly the button contacts would not be beefy enough for dual Fiamm horns, if they carry the current drectly, which it sounds like what happened, as it will be several Amps. I put Fiamms on my LM and definitely needed to use a relay. Why it didn’t work with the new switch I don’t know, maybe just a gremlin?
PS if you don’t like the ‘meep meep’ go onto Vehicle Wiring Products, look for ‘Compact Horn 12V’, no relay needed but sounds much more betterer (V7 850 has the same useless horn)
Thanks for that.
As I said in my post, the loads I was imposing seemed to be outside the settings as indicated by the working of the standard horn. The dealer did say that they won’t do anything to the wiring because of the risks to the system.
Can bus is a good system or manufacturers would not use it. I was just surprised that the relay method didn’t work but at least I have a logical reason for it.
the one shown on the site is different to yours, unpainted and made in Italy.
i have ordered one so I’ll see what i get next week
Yes, it changed! Not sure I like that. I expect it’s plated.
Again, I’d want to find out exactly how it was connected, and not assume. (No offence meant.) 
On the V7 850, twisted pair canbus leads connect between the ECU, dash, ABS unit and immobiliser only (and the immobiliser is optional, so on mine it connects to empty air), all else is ‘normal’ wiring.
it will get some black hammerite on before i fit it i think
I used the horn’s own connections to, at first, power the horns and when that failed used the same connections to power the relay for them. In effect I created an extra, separate loom just for the horns that was entirely independent of the canbus in the physical sense, using only using the horn supply for electrical needs.
Very strange and obviously frustrating… I hate the stock horns and the first thing I did when purchasing my V7 Racer ( 2013 new ) was to fit the two twin Fiamm horns and have never experienced any problems…
As I said, it is the black art that is can bus. A good system that has its own traits that are different and must be treated in other ways. I think that what I found might be got round by a resistor in much the same way as replacing tungsten bulbs with LEDs needs one, just that this is beyond me, technically, to try .
I don’t think I’ve ever used the horn, I’d better check it works before the bike needs it’s first MOT.
dont use the brakes either? 
Yes, use the brakes but never the mirrors!
the horn arrived, italian rather than turkish made and it’s unpainted/zinc plated. bigger diameter so to fit I will have to remove the beak because too much of a squeeze to fit past it even with steering on full lock.
I did manage to plug it in and test it and it’s a car horn sound not a moped meep 
Sorry if this has already been said but … have you tried to energise a relay from the OE horn connection, leaving the OE horn in place? This would piggy back the relay to the OE horn and cause a very small additional drain which may be acceptable to can-bus limits. In effect you could have the OE horn and the Fiamms all working together. The Fiamms would be supplied from the battery through the relay.
I took the operating feed from the two horn connections to the relay by simply using a couple of male spade connectors. I can see what you are suggesting but don’t feel inclined to go that far. I spoke to a “Tech” at the Peterborough show yesterday and the long and short (sorry) was that yes Can bus is a black art and many things are interwoven within the system meaning that alter one thing and several others may be affected.
Thanks for the thought though.
I bought one of these horns as well, I believe it’s too big for the V85 as it contacts the rear of the beak!
Am I doing something wrong? How did you get on with it?
Cheers.