needed for 6v horn

Idiot - you idiot! In answer to "Will a 30A fuse instead of 15A solve this?", I would have answered yes... IMO the horns burning out solves the problem. Let's see - 15A @ 12V = 180W, a reasonable amount of heat (excluding the 5% or so that gets converted to sound). don2rz - the problem with 12V is that the horns will be taking FOUR times the power (yes, 4x, not 2x). They will then burn out once they heat up. That could take linger than modern horns because of their bigger sized (more thermal inertia). Even if used for short bursts so they don;t get hot, they will probably fail due to repeated heating-cooling cycles (conductor fatigue; coils break etc). Although the coil winding insulation should handle 12V, its heating will cause it to break down as well. If 2 in series isn't good enough (compared to running each off a 6V battery), resistors are probably the way to go.... Or an adjustable voltage regulator, but you need to know the current for that. (Typically a $2 317k and trimpot with copious $2 2N3055s or similar to boost the current - maybe 3 or 4 for 20A; plus some other resistors & components.) Thanks to Idiot for looking after people's equipment. I sometimes get a bit evil, though usually only as a jest (though sometimes the jest is missed so therefore I caused damage... bad!).

Don, the above comment Idiot, You Idiot was directed at ME. 

An Overfused device becomes the fuse.

Keep in touch so we know how long it lasts.

I'm really not good at this kind of things but here's where I'm at so far... The 20A fuse is holding up at the moment (25+ honks) and still good. I'll try to keep up the count of honks lol. Hopefully it'll last long and better yet not damaging the horns itself.

When should I get the extinguisher ready? When I poster runs out of fuses and decides not to use one? This is a complete waste of time and moreover a fire risk, oh well I've said it, back to being demoted to Gold membership. Wouldn't it easier to replace the factory horns with Fiamms, or even air horns; all 12 volts and no fire risk.

No demotion! You are very correct. Maybe I/we should have emphasised that danger, though I thought myself "clear" in my "Idiot you idiot!" reply (above, top). But no harm emphasising or clarifying (as Idiot Esq did clarifying that I meant ImAnIdiot as the idiot, NOT the OP! But that was part of the jest anyhow... I'll stop digging my hole now.) If there were any suggestion of not having a fuse, then I too would simply pint out that that means a wire or horn or switch melt & VERY likely fire. Etc. Same with a fuse that is too big. If the horn blows, then it will probably be a very hot horn. The wires inside could be red-hot (or would it be white hot?). Runaway meting and it's a molten metal blob from +12V to ground. That's when the wire or ground bolt melts, or battery explodes... Yes, I too call that a bluddy irresponsible hazard. On the the hand, assuming the OP is well aware of the above and has cables and bolts & a battery that exceed the horns' fuse, AND a fire extinguisher, and is prepared to lose the horns, then IMO fine. (Somehow I got the impression don2rz was ok and would probably monitor hotness etc. But that is my bad - and there are other readers too.) Being an "old" Chevy & 6V may mean it is over-designed - ie, heftier than it need be (as was typical with most American and Jap stuff - like wiper motors, horns, starters etc), hence it may last long enough and fail gracefully (ie, thermal-fatigue open circuit or fuse melt). Though as I wrote, 12V for a 6V horn means FOUR times the power - ie, heat. And please note that I added a FIRE EXTINGUISHER to the above. It was irresponsible of me not to have mentioned that detail before. (Plus I have one or 2 in the car. I even had one on my Ducati's maiden road trip!) Is Titanium above Platinum? I'm merely considering the promotion of Howie.

This is not a horn, but it closely resembles what can happen.

Craig, though I use the live and ground leads sometimes to test which speaker and and it's phasing rather than a meter or an AA battery don't you think this was taking it too far?

Sorry, but how did he get his name?    (I know - he uses other people's examples. Clever genius!)

Howie, we really have no idea how this happened.  He claims that he put the amp in and the amp made a strange noise so he removed the power fuse from the amp.  Claims this happened overnight when there was not even a fuse in the amp.  Door speaker on same channel was damaged as well, it just did not catch fire.  He claims the rear fire put itself out.

A late reply (sorry!), but I just couldn't resist. And I finally found it: With thanks to mp3car's 2k1Toaster. (It is Royalty-free for now LOL!) NOTE - the above was hastily drawn by 2k1Toaster to get a point across to an other on mp3car.com I'm not sure if 2k1Toaster is embarrassed by its use, but he has certainly been surprised by its use - it seems to have cult-status on mp3car, or is it just that we regulars tend to crack up every time someone lobs it in? AFAIAConcerned, the pic conveys the hazards with inappropriate wiring - in this case, powering (too much) from cig-sockets etc. Maybe I should commission 2k1Toaster for a "speaker" or "12V into 6V horns" version?    Caveat: mp3car & the12volt and the aforementioned or involved contributors make no claims as to the technical accuracy of the above informative drawing. (However, I suggest i am an idiot's photo is technically accurate.)