How to add an auxiliary input to your car stereo



  • Older cars built before 2004 usually don’t have auxiliary input jacks. If your car doesn’t have an aux input jack then you can purchase a cassette player adapter or FM transmitter to connect your player to the car.

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  • Make playlists to avoid switching songs whilst driving. Be safe, concentrating on the road should be your number-one priority.

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Optical Connection


Many European vehicles, such as Porsche, Mercedes-Benz, Range Rover, Audi, BMW, Aston Martin, Jaguar and Bentley, use a digital fiber optic bus communication system called MOST for multimedia and audio transfer. MOST stands for Media Oriented Systems Transport. This fiber optic system handles audio signals between the radio, Bluetooth, and iPod modules and amplifiers. In many models of the vehicle brands listed above, we can add an in-line module that provides a stereo auxiliary input. No need to replace the expensive radio. Just connect to your smartphone’s headphone jack and enjoy.

If you want to see if there is an interface available for your vehicle, check the NavTV website under the Audio Interface tab.

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Step 3: Removing the Head Unit

For me this was as easy as pinching 2 clips on the sides together and pulling it out. Some head units will probably be a bit different from this especially if they’re not stock, but from my experience it’s usually pretty obvious. If not, then a quick search online will show how to do it on your particular car.If your head unit was like mine then you’ll want to unplug the smaller group of cords in the back. That’s the one our little black box is going to split.

RF Connection

For decades, one of the most popular methods of feeding and audio signal into a radio that didn’t have a dedicated auxiliary input was to use an FM Modulator. These devices would take the audio signal from your media player or phone, and transmit that into your radio via the FM receiver. You would turn the modulator on, tune to a specific radio station (which is selectable so it doesn’t interfere with a local station), and voila – you could hear your music. These are still available when a wired connection is simply not possible. The sound quality is limited by the FM receiver of your radio, but it’s better than listening to your music via the speaker built into your phone.

Step 5: Finishing Up!

So all that’s left to do is mount the toggle switch, make a hole for the cord, and put the face of the dashboard back on.First lets start with the toggle switch. Like most of you I didn’t tick every available option box on the SUV when I got it, so I have a handy blank space under my rear hatch button which I can mount the toggle switch to. I marked the center and used a 1/4″ drill bit to make the hole. I don’t recommend drilling while it’s still attached, I was just trying to make it clearer. On the back of the blank square was some plastic molding for whatever button I didn’t buy that was getting in the way so I just used pliers to snap them off. After your spot is all prepared simply screw on the locking washer, washer, and nut tightly then move on to the remaining mini jack cord. Now just drill a hole wherever seems most convenient, (I had to use a 5/8″ bit for this one) I did it on the far side of the CD player so it wouldn’t dangle near the pedals, and pull the new cord through. Note: If you tie a regular knot in the cord on the back side then if it gets accidentally yanked then it can’t pull on anything else. Now just put the dash back in the reverse order you took it off, remembering to re-clip all the buttons, reconnect the battery, turn on the car and release the high quality tunes!Note: My stereo had to be set on the CD player, and the toggle switch in the up position. Your done! If you have any questions feel free to ask. Hope this helped you! Please rate, comment and subscribe for more great instructables!