Upgrading from factory to BM horn for Perodua Axia (DIY)

DIY horn installation as per standard instruction

Everyone will certainly have at least 1 thing in their car where they dislike no matter it is just some design issues, underpowered engine or terrible handling to speak off.

I have 1 thing that I disliked in my new car, the Perodua Axia, that is the horn simply because it sound so cheap and unrealistic.

Commonly Perodua cars are factory fitted with diaphragm flat horn which sounds like "peen! peen!" and people usually feels like riding a kapchai horn.

More expensive cars such as continental cars are fitted with BM horn which sounds like "pon! pon!" and they are louder and nicer to hear.

But first, let me have an introduction regarding this BM horn and where does this type of horn get their name from?

As far as I know the very early car manufacturer who implemented this type of horn is from BMW and it slowly proliferated to the others like Mercedes Benz, Audi and so on.

But actually the real name for this type of horn is called two tone trumpet horn.

The principle of this horn is there is 1 pair of trumpet horns operating simultaneously at different level of frequency rate and it is usually a tad louder than diaphragm flat horn.

BM horn is just an industrial nick name given by mechanics referring to those horns that only can be found in some higher end luxury cars, BMW specifically and thus BM for short form.

But nowadays this type of horn is very common and can be found in any aftermarket accessories shop and fitted by 3rd party installer if someone prefer to upgrade their car horn.

When I first get my Perodua Axia half year ago and the initial moment I press the horn both me and my wife hated so much this kind of horn because of its sound so unpleasant to hear.

The horn sound so childish and not strong enough to shaken other people unlike my another car, Proton Persona which already fitted originally with a pair of BM horn.

But do you know that all horn can be converted to the type that you favourite?

So last month I have made up my mind to upgrade the horn to be sound similar to my Proton Persona's horn.

As usual, I had went to 99 car accessories shop around my home to shop for all the necessary items.

The first and foremost item is none other than the BM horn which I have choose Hella considering it is from a well renowned brand.

Supplement items included are a 12V relay to switching a direct 12V current to the horn and a single fuse box unit to cut off if there is power surge in the system.

All these items cost me a total of RM53, RM40 for the horn, RM7 for the relay and RM6 for the fuse box.

Next, is of course to study and understand the whole wiring connection from the car battery as the power source with triggering signal to the pair of horn.

Instruction for installation is provided together in the package to guide user on how to connect all the wiring and sample on how the system works.

A simple connection schematic diagram is also displayed on the packaging for an instant reference for the trumpet horn.

After that, I try to find where is the current location of the car horn and upon opened the bonnet it is very obvious and catch my eyes that the horn is just located right next to the bonnet hook above the front suspension upper strut mount.

And then, I also was planning to look for the best place to fix the new BM horn around the engine bay and to my surprise I manage to spot another existing horn behind the front grille next to the right headlamp.

This has prompted me to revise my plan immediately to add in a second piece of relay for triggering signal from the second horn as out of my imagination this car is equiped with two horns instead of one.

So I had gone back to the accessories shop again to get another piece of relay.

"Haih! unnecessary job..."

At last, all items are readied accordingly as per planned and next is to carry out work to find the best spot to place this new BM horn.

After some considerable time looking around and finally I have picked the best and sweetest spot to fix this new horn that is on the screw securing the front bumper just behind the number plate holder where this opening have a very large space to work around.

Not to forget to look for the battery power supply and a place to attach the small fuse box unit where I have selected to place it right next to the main fuse box inside the engine bay.

I have go on to develop my own wiring diagram using 2 relays because this car does comes with 2 horns and each existing horn will be switching 1 relay to trigger each of the BM horn.

Serious attention should be taken for the numbering on the bottom of the relay when connecting all the wiring and any wrong connection will short circuit and damage the car wiring system.

It is very expensive and headache to replace the original wiring harness and normally insurance company will not cover for such accident due to human negligence.

Next step is to carefully cut and measure all the length needed for the wires required and I have selected different color code for each connection within the system.

Then I also have designed my own mounting for this pair of BM horn by modifying some brackets and so I have went for some nearby hardware shop to purchase my desired bracket and screws with nuts.

Since the BM horn have its own steel bracket, I have to follow its own hole size at 8mm.

Knocking and drilling the brackets is not an easy task and please wear protective equipment for safety precaution.

And finally after some hard work done on my own bracket then next I am able to attach both BM horn to the bracket mount later to be fix on the back of the car bumper.

On the very next day, work started to mount the horn and join all the wiring altogether.

First is to take out the front plate holder and remove the front bumper screw to fix the BM horn unit together with mounting bracket.

Connect the wires to the BM horn and mount the bracket to the front bumper screw hole just now and fix back the front bumper screw.

Remember to stop the engine and let it cool down before working around engine bay area to avoid skin burn.

Connect all the wires accordingly to the pin number at the bottom of the relay and again please take serious attention when dealing with car electric circuit.

Also I have forget to mention to buy an 6mm cable lug for the small fuse box wire to attach to the positive terminal of the battery and connect this final connection to the relay to complete the system.

Initial testing was conducted to the new BM horn and my heart was suppose to feel happy but again and again something unexpected occurred out of my imagination.

The first problem is this car is fitted with two horns instead of one which I did not expected and the second problem that is also the biggest problem is both of them are purposely split to serve different functionality.

The horn located on top of upper strut mount of the right suspension is actually working as the car central locking alarm speaker!

I have tried to disconnect its cable from the existing horn on top of the upper strut mount and connect it to either one of the relay and the signal did not trigger the horn eventhough the horn button is pressed!

Frustrated about this I went to test both input cable between the horn at the back of front bumper grille and the horn at upper strut mount using a multimeter and found out that only the front grille horn cable have incoming 12V signal while the horn at upper strut joint is having no signal at all when horn is pressed.

It is very obvious that Perodua Axia is having only one functioning horn and the other one is an alarm horn and again and for this last time again I have to revise my plan to connect and switch on both horn only by using one relay and not two as I hope previously.

"FFAAAARRRRRRRRRRK!!!!!!!"

In this very final moment I had sat down and amend everything according to the need and while I have two relays to occupied with, this time both will be put into good use.

One of the relay will be switching the BM horn and the other one will be used to switch on both existing diaphragm flat horn to function as the alarm horn.

By this means, the current horn at the back of the front bumper grille will work as alarm horn same as the horn at upper strut joint.

So I had to redo again all the wiring as per requirements to utilise two relays to switch on two pairs of horns or four horns. Yeah!

After all the hardwork done to complete all the necessary new wiring I had went on to test this new system pending confirmation to secure everything in the engine bay.

"Yes! This last round all is working as per plan..."

When all these have tested to work perfectly and now it is time to do cable management by nicely tie all the wiring as tidy as possible inside the engine bay.

The stock cable and connector are still retained and I don't even want to cut the original wiring as I can revert back to the old setup at anytime I want.

Finally, my Perodua Axia not only have upgraded normal diaphragm flat horn to BM horn but also have two factory horns working as alarm speaker as opposed to one before this. Haha!

All the money, time, effort and hard work spent for me is worth the meaning for this project at last and now both me and my wife likes this new horn very much.

Below is the video for the loudness comparison before and after changing to the new BM horn.

A simple test was also conducted using my personal mobile phone installed with sound level test app and comparing both of them at a minimum distance of 2 feet up to 20 feet.

Mobile apps by "Abc Apps"

Result for both horn did not reveal any significant differences between these 2 horns if object is just beside the car but when at a far distance of 20ft away from the car the BM horn did register an improvement of +4.2% loudness over the factory horn.

Hope everyone will enjoy the new BM horn and two alarm horns in my new Perodua Axia.

If you need any clarification and have anything to say kindly leave it down in the comment section below.

Thanks for reading and hope will help those who are going to start the same project as well.

Or continue reading my next article about maximising my Pentair centre console box space HERE.