Eunos / MX-5 / Miata horn upgrade: Sebel Nautilus air horn

6 04 2010

The factory Eunos / MX-5 horns are a little anaemic.   So I had a look for something a little, well, sportier, and came across the Sebel Nautilus Compact air horn. It’s a twin tone one, and it’s of similar size to the Mazda horn, so I thought it worth a go. Cost me about 20 quid delivered – same as this one:

If you want one in a hurry then Halfords also carry them at a small premium.

First of all: disconnect the battery in the boot carefully.  You don’t want to accidentally short anything.  Make a note of any radio codes etc before removing the power.

Next, remove the old horn.

Open the bonnet, and look down between radiator and grille – you’ll see either a bracket with a horn attached on either side of the bonnet latch, or a single one on the right hand side. My 94 came with two. The bolt’s a 10mm one, so undo it with a ring spanner, and lift out the horn. There’s a single spade connector to unclip and it’ll come right out on its bracket.
The bracket is made of two metal strips bolted together in the middle. Undo middle bracket, and remove the old horn and the short strip of metal bolted to it, and stick it in your parts bin. Retain the other strip of metal, and bolt it to the Sebel using the square nut and matching bolt that it comes with. If you’ve got a grille fitted, now is a good time to take it out as the only hole it’ll fit through is the smile of the NA.
Make sure the horn exit is at the front and at the bottom so any water that enters doesn’t go in and sit in the horn body.

Next, we need to wire in the supplied relay to give a switched 20A supply to the new horn.

Note that you can fit these horns without using the relay – lots of guides suggest increasing the amperage of the fuse that powers the horn/rear sidelights/automatic gear selector and using the existing wiring.  It’ll probably work, but it’s not a good idea.  Using the relay is the Right Thing To Do, and is also easy.  If you need any more convincing then it’ll also prevent the risk of electrical fires/melting wires and sound louder.

Here’s a diagram of what you’re working with.  Note the ultraclean engine-bay, courtesy of Mazda Mender and his magic.  Cheers dude.  I’ll try and keep it clean.

You’ll need a length of automotive insulated cable, an inline fuse holder and a 20A fuse.  Solder the inline fuse connector to approx 3 feet of insulated cable on each side, making sure there are no bare connectors when finished – if in doubt use electrician’s tape to insulate.

Standing in front of the car, you’ll see a fuse box top left of the engine bay – see diagram above.

If you look closely, you’ll see a small plastic cover that you can unclip with a fingernail – behind this is a 10mm bolt that connects to the +12V supply for the car.  Attach one end of your new fused cable to the nut and tighten the nut back down to make good electrical contact.

Route this wire carefully down the inside of the wing to the front of the car, using cable ties to secure and ensuring it doesn’t foul any moving parts.

Take the red plastic electrical relay supplied with the air horn, and wire the +12V feed to the other end of the +12V feed from the fuse box by soldering/crimping a spade terminal to the horn side and pushing firmly onto the contact on the relay.  Attach the ground terminal on the relay to the mounting bolt for the horn bracket using a short length of wire with a spade terminal on one end and a ring connector on the other: the mounting bolt for the horn bracket secures this to the earthed body of the car.  Once done, wrap the relay in electrician’s tape to weatherproof.  The supplied relay has a convenient bolt hole to mount the relay – Imounted this to the single bolt attaching the horn bracket – see pic.

Connect the old horn wire to the switched +12V connector on the relay, and using a short length of wire with a spade connector one end and a ring connector on the other, attach the earth connection on the horn to the horn bracket mounting bolt as before.

You should now find that pressing the horn sends switched 12V to the relay, which then supplies up to 20A direct to the horn.  Don’t test it at 10:30pm, like I did.  The neighbours don’t like it.

I chose to leave one original horn connected in parallel: that way a short tap on the horn sounds the original one, and a longer one sounds both – the compressor on the new airhorn takes a fraction of a second to spin up.

The new horn mounts really neatly with space between it and any metalwork.

Now to test: warning, it’s 139Db, it’s very loud, and it sounds a bit cheeky and italian!
Job done. Very happy with it, it sounds great and it’ll definitely get you heard…

Update: since fitting this, it’s saved me from at least two near misses – both times when someone didn’t see me indicating and exiting a roundabout, and they set off in front of me.  They certainly heard me!


Any work you do to your car is entirely your own responsibility. If in doubt, you should check technical advice with an independent , qualified person who has seen your car.  I accept no responsibility for any damage caused to your person or property as a result of you following or not following the advice offered on this forum.




3 responses

17 11 2010

Cheers LW,

Once again your insight saves me blowing up my car!

Very useful blog 🙂

27 03 2011
Mazda 3 Horn Upgrade | Mazda Photos Blog

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12 05 2011

Hi – Thanks for such a good write up on installing the SEBEL. Put one in this afternoon and, appart from a trip out to buy a 10mm box spanner to get at that bolt in the fuse box, no problems. Thanks for taking the trouble to spell it out so clearly.

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