I'm not positive on this, cos it's really been quite a while since I swapped out a 2012 RT's horn, and there's a chance I might be confusing it with the 2013's I've done a few of more recently, but I
think you'll find your horn inside the tupperware surrounding the frunk, sort of above or maybe more just alongside the 'tunnel' on the right hand side of the bike (when you're sitting on it).
IIRC, to get at it, you'll need to take the frunk off (and disconnect the horn wiring when you do) then looking in from the back of the frunk (possibly after removing a plastic cover over the gap?!) you should find the horn on a bracket in the cavity that's found between the frunk tub and the outer tupperware. There's a fair bit of room in there, plenty to add another electric horn if you want, maybe even enough to put in an entire 'compact air horn' - quite a few Spyder Owners have done that, but it does depend on how 'compact' the horn is - the compressor & tank for my 'train horn' doesn't quite fit in there as well as the trumpets, so whenever I take the frunk off, I not only hafta disconnect the horn wiring, I hafta disconnect the air lines too.
But like I said, it's been a while since I've done a 2012, and my 'forgettory' tends to work a whole lot better than my 'memory' on things like this these days...

The Docs tell me that this is just a part of growing older, and that everyone hasta put up with it; only then they go on to say that the brain injury caused by being 'too close to too many explosions that should've killed me' back when I was wearing a uniform
juuust might not be helping...

No kidding!
Anyhoo, I hope that helps, and that I haven't sent you down the wrong path. Good luck!
