I've a bunch of Altette looking horns bought for very little, I've been meaning to get around to see what's involved in fixing them and making them correct for A10s, probably they are mostly from cars, some 6v some 12v, it seems the parts are available (bezels, dome nuts etc) to make a correct "HF1234" starting with Morris minor horns, but I've yet to work out if this is true or not!
What is "correct" Altette Horn for our bikes I've not established for sure, eg shape of main body, chrome bezel or not (some I've got have alloy bezels that would polish up nicely) special chromed domed nuts or not, bezel diameter, shape of vibrating disc etc, does it vary by year etc. I would be interested to know if anyone out there does know the correct spec.
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Car horns are of course generally 12v but this is not a problem when a 12v conversion has been carried out. From what I've heard a 6v horn works fine on 12v but not vice versa.