We all know that the stock horn on the 3 is a bit wimpy / pathetic.
I've actually gotten in the habit of only hitting the LOCK button on the remote one time when I leave the car; pressing it twice makes the horn chirp, and I would feel emasculated if one of the women at my apartment complex were to hear the pathetic sound that the stock horn makes.
I decided to upgrade the stock horn by adding a second, lower pitched, horn. It took me quite a while to figure out how to do it, when in reality upgrading the horn is quite simple. (And you don't have to cut, splice, or tap any wires.)
What follows is a beginner's guide to upgrading wimpy the stock horn in the mazda 3.
For starters, you will need some tools. Here's what I used:
Regular sized Phillips screwdriver, 10mm socket, 12mm socket (worked, but was a bit loose), flashlight, optional small flat screwdriver, and wire crimper / stripper tool
You will also need a replacement horn, some heat shrink tubing or quality electrical tape, some (perhaps one foot) 18 to 14 gauge wire (prefer 16 or 14 gauge), and a single crimp-on spade terminal that matches the one on the back of the replacement (or OEM) horn (this will plug into the factory wiring harness in place of the terminal on the horn).
The stock horn is just a generic, high pitched Fiamm AM80S trumpet horn, model A045622.
According to Fiamm's (the manufacturer) website, AM80S horns draw 5A of power. The fusebox has a 15 amp fuse, so I should be able to add a second horn and still have a margin for error.
I picked up a
Fiamm Freeway Blaster LOW NOTE horn at Advance Auto Parts for about $17 after tax.
Accessing the horn is quite simple, and if you have small hands and don't mind somewhat tight spaces, there is no need to remove the bumper. The horn is located below the driver's (left) side headlight (beneath / beside the air filter / intake).
You should probably put the front of the car on ramps or jackstands. There are three Phillips head screws that hold the plastic wheel-well piece to the front, left, underside corner of the bumper. Remove these screws. The flap will then be stuck underneath the skid panel (the one that gets in the way of the oil filter). You will have to slide it to the side to free it from the skid plate (Optional: you can also remove the skid plate if you like), and then peel it back as shown from the side:
Shine your flashlight up into the cavity, and you should be able to see the horn on its mounting bracket. There is a single wire attached to the stock horn - carefully unplug it. The bracket is held in place by a hook and a single bolt (~12mm). Remove the bolt, then slide the bracket upwards to free the hook from the chassis.
You will need to remove the nut from the stock horn on the bracket, and then add the additional bracket for the second horn, as well as the ground for the second horn. It might do well to put a bit of lock-tight on the nut (you might assemble the whole thing before tightening it down for the final time, however). Below are two pictures of stock bracket/horn with the additional bracket/horn added.
Stock horn
Additional horn (they look quite similar)
(UPDATE: people with fog lamps have commented that it may be necessary to re-hang the original bracket first and then bolt on the stock horn and the extra bracket/horn second.)
You will need to wire up a small harness to plug the stock connector into the two horns (they will be connected in parallel). The two female crimp connectors come with the aftermarket horn; you will have to buy an extra male/spade terminal that matches the ones on the horns and plug that one into the factory horn wire that you disconnected earlier.
Here is my harness:
Here is what it looks like on the mounting brackets:
At this point, you need to reinstall the horn assembly.
Be careful not to hit your hand on anything while tightening the nut.
You may have to readjust it a bit to make sure that your horns don't rub on anything in the vehicle. (I don't have foglamps, so i don't know if they make this process difficult or not - You might see how much room you have in there before you start)
Here are some pictures looking up from the bottom of the car at the improved horn assembly:
(the horns face toward the front of the vehicle, at a downward angle. The aftermarket horn is closest to to the camera/bottom of the vehicle)
The horn sounds like it belongs to a real car now; nothing to be embarrassed about anymore.
(Be sure to let us know how your upgrade turns out!)