Car Stereo AUX Input Taps Into CD Ribbon Cable

[Gezepi] wanted to add an auxiliary input to the stereo in his 1994 Camry. At first look there wasn’t an easy way to patch into the system. But a bit of probing with an oscilloscope and figured out that he could inject audio through the CD ribbon cable shown above. The CD reader is a self-contained unit that receives commands through the cable, and passes analog stereo audio back to the receiver portion of the head unit. We’re not sure how he figured out which pins to tap into, but it may have been as easy as probing with some headphones while a CD is playing.

The extent of his hack is documented in the image below. He cut the two audio leads on the CD side of the ribbon cable, then soldered his auxiliary jack on the receiver side of the cable connector. This ensures that two audio signals aren’t being piped into the receiver at the same time. Unfortunately it also means that he won’t be able to use the CD player. We have seen other methods that use a special audio jack as a pass-through which cuts the connection when a jack is inserted. That’s the method used in this Subaru hack.


50 thoughts on “Car Stereo AUX Input Taps Into CD Ribbon Cable

    1. That’s what i made to my vintage BMW. I am required by law to maintain it’s original state and therefore cannot (and will not) insert a modern stereo. So i tapped into the TDA chip and routed the connections out.

      1. Where do you live that it is illegal to even replace a stereo in a vintage automobile?

        I have heard of laws for “Historic neighborhoods” that attempt to limit what property owners can do to their buildings on the outside of them, to try to maintain the character of the neighborhood. However that only regulates the outside of the building not what happens inside, where anything goes. Have never heard of such laws for cars.

        1. Yeah me either. Modifying a vehicle does not affect its age. Once the chassis is older than 25 years it is an antique regardless. Although I have heard of use laws in order to maintain antique registration. Such as a miles logged per year limit. I believe it is 2,500 miles driven.

          1. It varies by jurisdiction. Some are 250 miles, some are more. Some can only be driven to car shows, maintenance, and the occasional personal drive (Penn is once per week at most), but not work. Tenn. Requires a cop to verify it’s in antique/classic condition before you get the plates. Some restrict aftermarket add ons. Penn requires a “classic car” be refurbished to original manufacturer specs AND appearance.

        2. I live in Germany, Exactly what derekb wrote, its a special form of registration. I am nearly tax-free and pay very very low insurance. But i have to preserve the state the car was in 40 years ago. I could however modify my vehicle to my liking (within law) but then i would loose my “historic registration” and would pay extremely high taxes and insurance fees. Additionalky a historic registration allows you to enter any city in Germany, where older cars are not allowed to enter due to emission. (“Umweltzonen”) High fines exist if you are caught driving in the city with such a car.

      1. Not necessarily. That radio obviously uses analog audio output between the cd player and the stereo, so while it could be digital audio output, why would the manufacturer bother? It’s a closed, embedded system, it only needs to work one way. The stereo still needs some way of controlling the cd player, (play, pause, stop, ff/rw, etc), and SPI is just as valid as any other protocol to use.

        Granted, there are 21 pins on the player side so maybe, but only 10? on the stereo side. I still say it’s possibly spi.

    1. If you’re willing to spend the time watching the mechanism, you can usually find where the fault is and get it to stick the one time needed. Be sure to remove the eject button prior to any of this, btw.

      I used to do something similar to “junk” tape decks in the early 80’s. Since I had to actually fix them fully for them to be usable, I wasn’t always successful but I did turn several auto-reverse decks into decks that would play the audio on the other side of the tape, giving me the ability to play audio backwards without tearing up my needle or my vinyl, which was much cooler IMNSHO.

      1. Ah, I had to wait for my first Soundblaster to do that. I did once somehow manage to “repair” a cassette to end up playing backwards, but that wasn’t on purpose.

  1. I did the same thing in my ’99 Cherokee’s head unit except I tapped it in to the tape player input on the internal amplifier; because I didnt like having a wire from the cassette adapter run out the front of it.

  2. I solved this problem myself by purchasing a head unit with multiple I/O… like 8 of them in total… A/V at that. (I actually think it’s more, but I only use a few of them)

  3. Yep! Did this on an aftermarket head unit I used to have. I just probed around on the main board for sound but couldn’t find a clear signal. The CD module had L, R, and GND clearly labeled right before the ribbon cable so that was the obvious choice. I ended up cutting the traces and using a DPDT switch to flip between aux and CD. Although the wires I used weren’t shielded so I heard a faint whirrrr when accelerating. You DO have to have a CD in and playing to hear any audio. An alternative to using a switch or special jack would be burning an entire audio CD of silence so just the aux plays out.

  4. Used to do this alot when I worked in an electronics shop. Mostly for mike inputs on school busses. They used the radios for P.A. systems on the bus. They fitted the buses one by one and for some reason, never used the same radio/cassette player twice. A new serch every time. To find a good input point you just need common sense, to be able to recognize components, and use a signal injecter. (touch it with a metal screwdriver with your finger on it, you will get a hum) Micky Mouse electronics, but it always worked.
    Pokeing metal objects into running electronics is sometimes a bad idea, but in car stuff, it’s only 12v

    1. I did this too, with the CD player that was residing in my POS dodge Aries. The thing had RCA outputs — I converted them to inputs. Had a CD with 74 minutes of cd-quality silence on it. As long as the disc was in the drive the amp boosted appropriate input and Ipod worked perfectly. It was a very simple project but I still felt like a god for a few weeks.

  5. congrats blowing countless hours of your life working on a pos stock stereo, you can literally buy the cheapest of the cheap headunit with aux in for 30-50$

    how much is peoples time worth like honestly? these “hacks” that keep popping up on here truly make me less and less interested

    this is sad

    1. It might have been a waste of your time to do, but I saw it as a great way to add functionality to what I already own and learn some basics about the oscilloscope I recently got.

  6. I did a simllar thing with my Corolla 06, i tapped into the ribbon part, but on there the stock head unit will override and play the 3.5mm, and CD at the same time, so i just flipped the CD upside-down and play the blank track. :D

  7. I did this as well in my old Saab 900, -95. I hijacked the tape-input on the mainboard and hooked up an AUX-cable. Con: I needed a casette in the player, but I just removed all tape from the casette, and then the player went on and on :=

  8. Five terminal stereo jack not a three term and you can interrupt any path, inserting what you plug in.
    Did this in mono in ’71 with my parents Olds hidden away under the lip above radio. A stereo jack included power for the Norelco first gen Cassette portable dictation machine.
    School bus kids listen to the radio?…With earbuds in they don’t hear that.

  9. Forever feeling betrayed by Hackaday when I pulled off this hack with a Ford tape deck, including having to try and figure out which microswitches were enabled in which order by a tape being inserted to switch the radio into tape mode. Only way I could do it because tapes inserted would get jammed anyway. It led to years of questions like “Why does your radio have an F6 key?” because I scrapped an old button keyboard for the parts.

  10. I’v tried a similar hack on my toyota 05,
    The soldering was good, but for some reason I got really bad audio from the left channel and no audio on the right. the regular cd player worked perfectly… Some impedance problem maybe?

  11. Yeah, or they’ve used different pins so you are feeding audio across both channels rather than differentially.
    I always check from signal to ground with meter, this has got me out of trouble a few times as even a cheap resistor on low ohms range will show a difference if the pinout is wrong.

  12. It is that easy although I question tapping the ribbon cable directly. The real trick is getting it in before the digital volume controls etc. did up a dead boombox for the wife’s ipod the same way and she loves it so much I am going back in to tap charging voltage for usb. Ended up using the tape bay to hold the shuffle when not in use :) Kudos to the builder for getting in there and figuring things out :) Don’t know why, but I have always been squeamish when dealing with car audio but that is due to inexperience on my part.

      1. Oh yeah, that is why. You are right about that. I love the interior snap(off) panel heads and resealing the weather lining/noise cancel garbage inside the door. Don’t even get me started on the dash lol. Talk about shoe-horning things in and out lol. Thanks for reminding me why I am squeamish :).

      2. Yeah, the worst part of the whole project was trying to figure out how to get the stereo out. After diving right in and getting no results I turned to my maintenance manual and it listed how to remove the radio.

  13. I did this by tapping into the radio ic, found a datasheet for the pinouts online. The nice thing is it even picks up when I’m playing something through the aux and cuts the typical radio interference (not sure why it does that, some kind of automatic gain maybe?)

  14. Thanks Hack a Day for posting this project, I’m famous now!
    To answer some questions/comments:
    I started probing the cd side of the ribbon cable and when I found an audio signal I realized it was coming from the pin labelled “L” and there was “R” and “Gnd” right next to it.
    The cd player needs to be playing for the sound to get through which is why I cut the ribbon cable. I also burned a cd with nothing but silence on it so I could reconnect the ribbon cable and it would likely sound alright.
    Initially there was noise when I reinstalled it so I took it back out and changed the grounding point to the one on the ribbon cable next to the L/R signals. It was nice to be able to verify that changing the ground fixed the problem by probing the amplified output of a sine wave and see only the wave instead of the noise that had been there.
    There are 20(21?) pins on each side of the cable. On the head unit side they are split so that even pins are on one side and odd are on the other (so hidden).
    There’s no cd changer option on this unit so I wasn’t able to tap into those. Another of my stereos had that which made it much more straightforward.
    If I take the thing apart again I’d like to see what is sent over the SPI pins and maybe get the audio to play without needing a disc in.

    Thanks everyone for all the comments!

  15. I want to ask from any that what purpose of 2 nos left (white) and right (red) female jack at the rear side of unit, either these are for input or output, and if these are input then can these use for usb, secondly from I get 5 volt supply for usb.
    and how to convert cassette player into mp3

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