Matt Gilbert

Car Stereo iPod Input Hack

Tutorial · May 14, 2007 by Matt Gilbert

I was tired of using a cassette adapter with my iPod, because it added lots of noise. If I tried to turn the iPod up loud to drown out the noise, the levels would get messed up somehow, and the treble would sound painfully loud. After looking around online for auxiliary input things you can install in your car, I found that they all ranged from $80 to $200, plus installation. While this may be nothing to some people, I thought that an aux input can't possibly be that big of a deal. So I poked around with my stereo and figured out how to do it while buying only a toggle switch that I got for 50 cents, and using some wires and stuff that I already had lying around.

I got sort of lucky, because my 2001 Corolla was a little easier to hack than I imagine some cars will be. I'm just using the factory system here, with no aux inputs built into the head unit and no amp or anything like that. The difference is, mine has a CD player unit that's seperate from the head unit. This means that there is audio being passed from the CD player to the head unit, and those wires can be clipped and redirected to other uses. I imagine any car that has a seperate CD player, CD changer, or whatever will be hackable in the same way I did. If not, then I guess you'll have to figure out some other way of doing it.

So the way I have it set up, I tell the stereo to play from a CD, and it does, but I switch out the audio with the audio coming from my iPod or other aux input.

Clicking on the small images will take you to larger ones, some of which have descriptions.

Opening the Console

  Here's the console. The upper part, with the AC vents, clock, hazard button, and main stereo unit, is the part I needed to remove. That little blank part that's the same size as the hazard light button doesn't do anything, so that's where the toggle switch will go.

  There are little slits on the bottom of this part of the console where you can poke in a screwdriver and pry it out.

  Like so.

  Do this on both sides, and you should be able to pull it out the rest of the way by hand.

  Like so.

  There are two connectors going to the hazard light and to the clock.

  Disconnect them so you can get the console part out of the way.

Finding the Audio Connections

  The back of the stereo head unit looks like this. The 2 harnesses to the right go to the speakers and other stuff in the car, and the harness on the left goes to the CD player. This is the one that we are concerned with.

  I didn't know any of the color codes for my car, so I had to poke around to see which connections were listening for audio. To do this, I had to start the stereo with everything connected in the back, and start playing from a CD. Once it started, I unplugged the harness connecting the CD Player to the head unit, and connected an audio cable from my iPod to each of these connectors until I heard something coming out of my car speakers. I did this one at a time so i knew which was right and which was left through trial and error. It will sound like crap if you only have the positive connected but not the negative, or the other way around, but don't worry because it will sound good once everything is connected.

  It turned out that the two green wires were the left channel, and the two grey wires were the right channel. A wise man who lives in a fairy castle once told me that it doesn't matter if the positive and negative channels are flipped, as long as the right and left channels are flipped in the same way.

Finding a Spot for the Toggle Switch

  Before clipping and soldering all these wires together, I planned out where the toggle switch was going to go. This unused hole in the console was perfect. This is how to remove the plastic piece stopping it up.

  I just pried this part out with a screwdriver. I manage to break a tiny part of it while doing this, but nothing that make anything stop working, and nothing visible.

  I'll save this piece for later in case I sell my car to someone who doesn't want the aux input.

Wiring the Toggle Switch

  I took this headphone cable I had left over from some other project, and wired this in to the toggle switch.

  Here's the toggle switch I found. Clicking on this image will show a diagram explaining how I wired it up a little better, but basically, the center part connects to the head unit, one side connects to the ipod, and the other side connects to the CD player. I got lucky when I found this toggle switch, since it's actually four toggle switches in one, so I can use it to switch the positives and negatives of both left and right channels all at once.

  This was the hardest part because I had to solder this stuff together in the console of my car. This is because I couldn't get the CD player removed from the console, so I had to work on it there. I clipped the green and grey wires leading from the CD player to the head unit, and connected to CD player to the toggle switch, and the toggle switch back to the CD player, doing my best to keep all the left/right, positive/negitive stuff straight. I used this audio cable that is 2-conductor and shielded mainly becau se I had some lying around. I don't know if the shielding is neccesary, but it can't hurt. It also helped me keep the wires well organized by pairing up the positives and negatives of each channel.


  I got lucky because the toggle switch I had fit perfectly snug in that hole in the console. I just have a headphone wire dangling out, which is fine by me, but I know some people would prefer a headphone jack so they could remove the cable when they wanted to.

So the way this works is you tell the stereo to play a CD, and it does, but you switch the signal that it's getting from the CD player to the iPod, or other aux input. Your stereo keeps spinning the CD, and it keeps showing the track number and time of the CD, and you can switch the audio back and forth from CD to aux at any time.

It sounds really good as far as I can tell. There's definitely no noise like when I was using the cassette adapter, and the levels don't get all messed up when I play the iPod loudly. (This is something that was happening a lot to me with the cassette adapter, but I know this doesn't happen for everybody.)


Update · May 14, 2007 by Matt Gilbert

Here's an update with just a few details.
First off, the toggle switch you'll need is a "4PDT" switch, or anything with the same spec with a number greater than 4.
The impedence concerns of one poster seem to be nothing to worry about, according to everyone I've talked to who has anything to say about it. The seperate CD player seems to pass a signal at line level, and that seems to be what the head unit expects. However, I'm not sure if I made this clear before, but this is a first time thing for me, so do it at your own risk.
If you're looking to do this on a system with a different set-up, this hackaday post will help you sort out a strategy.


Update #2 · May 14, 2007 by Matt Gilbert

Someone wrote me with some safety concerns everyone should know about. I don't know if any of this is true, but better be cautious, I suppose. I've copied his email here:
"I have a 2002 Toyota Corolla, so I know there is an airbag sensor just inside and to the right of the radio (it should be yellow). If you accidentally touch it or jiggle it, there is a VERY high chance the airbags will deploy likely killing you if your face is right there or at least breaking your arm.
"To deactivate the airbags in a Corolla, you first get in the car while it is just sitting there, put the key in, turn the wheels straight, turn the key to the Lock position, pop the hood, remove the negative battery cable by loosening the bolt with an adjustable wrench, and place it to the side where it doesn't touch any metal. After that you MUST wait 2 minutes or more for the capacitor to lose its charge or the airbags could still deploy (I actually recommend 5 minutes or so, go clean your windows or something while waiting). After that, you should be able to do most things without deploying the airbags. I wouldn't ever touch ANYTHING bright yellow under your dash unless you are very careful. There are several airbag sensors around the car, I don't know the exact location of all of them, but on a Corolla like our's there is one just to the right of the radio, one behind the glove compartment, one between the front seats somewhere, possibly one on the driver's side of the dash, and several on the outside of the car around the front and rear bumpers. You should make sure to disable the airbags when working on just about anything, it is better to be safe than sorry or dead.
"Oh, and for those who have anti-theft radios, they need to know the code to unlock their radio before detaching the negative battery cable or their radio with be locked and not able to function until the code is entered. If that happens, the person would need to take the car to the dealership to get it unlocked most likely."

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