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Discussion Starter #1 (Edited)
Vehicle: 2014 Mazda 3 Sport GS (Canadian mid-level trim)
Time: ~ 1.5 hours
Tools: Wire Crimper, Cutters, Electrical Tape, Socket wrench, 10mm Socket, Tape Measure, Impact Gun, 13mm Impact Socket, Dielectric Grease
Hardware: 12 AWG wire, 2 x grounding rings (3/8"), 1 x male connector (1/4"), 4 x female connector (1/4")

Everyone knows the horn situation on the 3 is pretty sad. With only one low tone horn, don't expect to get any attention from other drivers.

My first encounter with this issue was on the highway when some chump started cutting into my lane. I honked, but I don't think he acknowledged my presence and continued to obliviously cut in front of me.

The inevitable happened last weekend when a truck backed into me and rammed his hitch through my front bumper even through my various failed attempts to stop him. Aside from him being a complete and utter moron, I felt that my horns did me no justice in my time of need.

I quickly opted to purchase some Hella horns to unleash my hatred upon the world with the sweet justice of a piercing 118 dB to vibrate the ass hairs erect on the next douchebag that wishes to back into me.

I purchased a set of Hellas off Amazon. At $57 with free shipping, who was I to say no?


After reviewing the horn wiring diagram for the car I decided to wire the horns directly to the OEM harness and ditch the relay that came with the horns. As you can see in the below diagram the horn already passes through a relay and to a 15A fuse. The Hellas draw 5.5A each horn. As they're wired in parallel, the total current will be 11A which is still within the safe operating range of the existing circuit.


If red isn't your thing, simply unscrew the 'cage' off the horns and spray bomb it with your favourite colour. I went with a less conspicuous black followed by a couple coats of clearcoat.


With the cage off, you can see how the horn looks under the cover. This is also a helpful way to identify the ground terminal and the power terminal on the horns. The long metal plate on the inside of the horn is the power side, while the other side is the ground.


With the horn flipped over, this means that the power terminal (circled in red) is on the left and the ground terminal (circled in white) is on the right when the terminals are oriented in the 12 o'clock position.


I took the bumper off first and found my mounting points before I made any wiring. But since I've taken out most of the guess work for you guys, you can make your wiring first!

First make 2 grounding wires. Take your 12 AWG wire and cut 2 x 4" pieces. Attach a female connector to one end of each wire, and a grounding ring to the other.


Next you're going to make your power wire. Take your 12 AWG wire and cut 1 x 9" piece and 1 x 24" piece. My wiring ended up being just right with no slack so you may want to add an extra inch to each piece.


Tie two ends together and attach a male connector, while attaching female connectors to the two free ends.


You are now ready to remove the bumper. I followed the service manual for this and it was my first time removing a bumper on any car. It took about 30 minutes with me and a friend being careful along the way. With the bumper off, you will immediately see two very prime mounting locations.


Pull the connector off the stock horn, unbolt it, and chuck it across the garage.


The Hellas come with 3 mounting brackets stacked on top of each other. I had to use an impact gun to take the center bolt off in order to remove one bracket off each horn. You should only need 2 'layers' of brackets on each horn.


Now plug in your grounding wires to the identified grounding terminal on the back of each horn. I put a dab of dielectric grease on all of the electrical contacts.


Hand tighten the horns onto the identified mounting points, using the existing bolts to hold down your grounds (it'll be the same for both sides).


Now plug the male end of your power wire into the OEM horn harness.


Take the two female ends and plug them onto the power terminals on each horn (the lower terminal in the picture below. Same for both sides).


Now tuck those wires! I clipped my wiring in that little gap you see circled in the picture below. Both sides have these convenient little clips as you can see in the above photo. If your wiring is tight enough, the long 24" piece will conveniently tuck under the rad support.


Now tighten down the horns and make sure they're straight. Test them (make sure nobody is standing in front of the car), then giggle like a little girl.


Put the bumper back on, and voila!


Remember, don't let this happen to you:

Upgrade those horns!
 

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Great project!

Sorry about your bumper. Speaking of which, how hard is it to take off the bumper? You did it with a friend, but is it something you could do alone?

Also, what size grounding rings and female connectors are needed?
 

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Discussion Starter #4
Great project!

Sorry about your bumper. Speaking of which, how hard is it to take off the bumper? You did it with a friend, but is it something you could do alone?

Also, what size grounding rings and female connectors are needed?
The bumper is pretty easy to take off, it's about 25 screws and clips holding it on (wheel liner, undertray, and "set plate" under the hood). Just be careful in the areas where it meets the fenders. You can do it yourself, but it's easier to have another body help guide the bumper off and on, as well as holding the bumper while you unclip the connectors for the turn signals and fogs.

I used a 3/8" grounding ring, and 1/4" female/male connectors. I updated my original post for clarity.
 
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Discussion Starter #6
Excellent write up. Thanks for takin the time to do this. Right thumb!

Did you use the included relay and run power to the battery?
I didn't for a couple of reasons:
Firstly the OEM system has a built in relay, and 15A fuse for a 11A draw from the horns. Secondly, I understand that running power off the battery optimizes the sound of the horns, however I wanted to keep the wiring under the engine bay clean and minimal. I did my HID's at the same time which used a relay harness. I didn't want to run too many auxillaries off the battery.
 
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Awesome...thanks for the write up! This is a project I was planning to do this spring and now it will be much easier.
 

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Edit...went with the ones you installed after seeing how much more powerful they were (118 dB) than the Hella horn-style (110 dB). That's a major difference.

Nice writeup, thanks a bunch!
 

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Forgive me for not knowing anything about swapping horns, but is this about as simple as a horn upgrade gets? I guess I envisioned just swapping out horns and not having to change wiring or anything
 

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Forgive me for not knowing anything about swapping horns, but is this about as simple as a horn upgrade gets? I guess I envisioned just swapping out horns and not having to change wiring or anything
For the most part. Each application would require you to take a look at the car's wiring system to make sure it can handle two higher-current horns. Most new cars use a relay to send power to the horns, so smaller wire can be used through the horn switch to trigger the relay. Check for a relay and see how large the fuse size is for the horns. If the total current draw for the new horns is lower than that of the fuse by a few Amps, you should be fine. You'll have to make up some little jumpers for power wire but that's about it.

I did this last year on my wife's '01 Galant and basically did the same thing the OP did in this writeup. Most cars can handle much better horns with no problems.
 

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Excellent write up!

My apologies in advance for the newbie question but is it necessary for me to remove the bumper to replace the horns or is there any other way to do this?

Thank you!
 

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I checked and it doesn't look like you can avoid taking off the bumper unless you want to mount it in the engine compartment.
 

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Discussion Starter #13
I checked and it doesn't look like you can avoid taking off the bumper unless you want to mount it in the engine compartment.
Agreed. I thoroughly checked the car to see if I could do it without taking the bumper off. I thought maybe the rad plate (aka set plate) would give me access if I removed it, but it doesn't at all. The grill can only be removed from behind the bumper so there goes that option as well. Don't be intimidated, the bumper is easy to take off. Just take your time with it to make sure you don't scratch the paint. I was lucky enough to have a hoist, but driving up on ramps or jacking it up would be simple solutions.
 

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lay down furniture blankets or something similar underneath ALL of the bumper. I fold them (or wad them) a bit so they sit flush with bumper. It won't fall at all, just pull forward. Then you can prop something (I use road cones) against the license plate to keep bumper stationary but pulled away for access. Hella install required me to unplug one fog light and twist bumper 90 degrees to allow for work down low under crash bar. I was sketched trying this the first time but have done it twice now and won't worry about needing a buddy to help in the future.
 

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Agreed. I thoroughly checked the car to see if I could do it without taking the bumper off. I thought maybe the rad plate (aka set plate) would give me access if I removed it, but it doesn't at all. The grill can only be removed from behind the bumper so there goes that option as well. Don't be intimidated, the bumper is easy to take off. Just take your time with it to make sure you don't scratch the paint. I was lucky enough to have a hoist, but driving up on ramps or jacking it up would be simple solutions.
I took a real quick look today on removing the rad plate or slip plate as they call it and looks like it can be removed. Didn't have time to really get into it but may take a closer look tomorrow or Monday. The Miata gets priority if the weather is good as I have to change the differential oil soon before I put it back on the road for the summer. Can't wait ! If it is easily removed will be heading down to the Auto Wreckers as soon as it dries up. Had my eye on a pair of horns off a newer Ford F150.... nice tone and loud. Best part ; about $6
 

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Discussion Starter #17
I took a real quick look today on removing the rad plate or slip plate as they call it and looks like it can be removed. Didn't have time to really get into it but may take a closer look tomorrow or Monday. The Miata gets priority if the weather is good as I have to change the differential oil soon before I put it back on the road for the summer. Can't wait ! If it is easily removed will be heading down to the Auto Wreckers as soon as it dries up. Had my eye on a pair of horns off a newer Ford F150.... nice tone and loud. Best part ; about $6
The set plate is easily removed but it won't give you enough access to install the horns.
 

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That was what I was wondering ; but will take a closer look today or tomorrow ; as I know that the working room on the Miata was tight but was able to do it . Thanks .
 

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Hell yes !. I need to do this and all will after they have dealt with dumb asses cutting you off and our weak ass horns doing nothing to cause attention or warning.
Could you please post a sound clip or a video of what it actually sounds like now. ?.
I'm not entirely sure which hirn to go with, so a sound clip or the like would make my decision a lot easier.
Thanks.
 

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Nice, I did this install about two weeks ago; I was pissed because only 1 of my horn had the brackets on it (each horn is using one bracket) and the mounting bolt was missing.. got what I needed at home depot and got it installed. They sound corny when you beep the horn when you lock it, but when youa ctually use it they sound good.
 
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