Hi all,
I’m converting my DT400B to 12V. The horn in the ‘accessory pack 4’ from Rex’s Speed Shop isn’t suitable. The fixing screw on the back of the new one is 7mm long. The fixing screw on the old one is 11mm. That difference is enough to make the new one not fit onto the existing bracket.
Yes, I could bodge something, but would prefer to buy a horn with a longer fixing screw on the back.
Has anyone out there been through this pain?
Can anyone recommend a suitable 12V horn?
I’ve (hopefully) attached pictures showing the different lengths of fixing screw and the bracket that the horn has to fit to....
Sorry my posts are so boring at the moment!
Many thanks, Phil

I've just used the 6v horn with 12v.

I did the same, use a 6v, it's loud. 
Way back when, converting VW to 12v, the old beetles with semaphore turn signals were 6v, they would flip up so fast the car would tilt,  , LOL 

The 1974 DT125a is 12v.  I just put one of those on.  Admittedly I haven't finished the bike yet so I can't say if it works or not.

vic

I chuckled to hear MD Scott's thread re: fast operating semaphores on old cars. My dear old now departed grandpa used to have an old Austin that had semaphores (for you younger members that's indicators that popped out on an arm..!! ) and they fascinated me as an inquisitive boy.  Wind forward 55 years that same inquisitive nature has now given me a problem. You see I too have upgraded my bike with a Rex's 12volt conversion but have not got to fitting the new horn yet.  Trouble is my curiosity made me take the old 6volt horn apart (mutilate) just to see how it works. Arrgh..!!   The new horn mounting screw does indeed look very short.  They say you 'live and learn' so the moral of this story is "if it's not broken save it"
 

I queried this with Rex's Speedshop. They said that they have never seen this issue before.
Looks like it's just me that has a standard 1975 DT400 horn bracket that I can't buy a new 12v, 1.5A horn for then....

I wouldn't count on Rex as any sort of authority on the topic. You have a common Yamaha horn mount.  What they sell simply isn't correct.

Spending one minute on Yambits found a likely quality replacement in 12v.  They have several others that may fit, this is just the first that caught my eye.

yambits.co.uk/rd400e-usa-horn-12v-nikko-...nkim9blum1g55guvavd6

It's got 1.5A in the description, but 2.5A stamped on the horn in the picture.

I'm not sure why that matters?  But I guess you're right.  You're very unlucky and you'll never find a 12v horn that suits your bike. 

You could try one of these universal models.

dratv.com/12volthornassy.html