I have a Gamma radio with the six CD changer underneath it.
The problem is, the radio must have data communication with the CD changer to allow the left and right audio channels to remain open. If it doesn't get this data feedback, it'll switch back to FM or whatever. So you need to fool the radio into thinking it's receiving the audio channels from the CD changer. It has no idea if you tap into these wires.
So all you need is a 3.5mm break contact socket and a lead with 3.5mm plugs either end and a dab hand at soldering!
Basically all you need to do, is cut the audio channel wires on the CD changer plug and place the socket between CD changer and the wires you cut from the plug. What happens now, without a plug in the socket, the wires you cut travel through the socket back to the radio like they'd never been cut, allowing the CD changer to function as normal. However, now if you insert a plug into this socket, it breaks the audio connection between the radio and the CD changer, allowing your MP3 to send its audio to the radio instead. Since the data is still being sent to the radio, you need a CD in the changer for the radio to think it's playing it. However, of course it's not, the audio is coming from your MP3, or whatever you have connected to the socket.
I have extended my little socket to the glove box, should I want to put my MP3 player in there out of the way. However, I have a little Sansa Clip MP3 player, it's so small, it fits in the ashtray in front of the gear knob. So I have a lead connected to it running into the dash and into the side of the glovebox connected to my socket. Again, if I want to listen CD's like normal, I simply unplug this lead and the CD changer reconnects to the radio fully.
This is the socket you need. (You'll need to find out what is left, right input and output and ground on your own socket, it may be different depending on the brand..)
![Image](http://img.photobucket.com/albums/v605/Brind/gc33724.jpg)
The blue plug is the plug you need to modify. Cut back the heat shrink on the cable to allow more access and cut the wires in half that go to pins 18, 19 and 20. 18 is audio ground, 19 is Left audio and 20 is Right audio. Then simply wire the socket between the cut wires.
![Image](http://img.photobucket.com/albums/v605/Brind/connector.jpg)
![Image](http://img.photobucket.com/albums/v605/Brind/simple-diagram.jpg)
![Image](http://img.photobucket.com/albums/v605/Brind/35-socket.jpg)
I have an audio file you can download and put on your MP3 player to check the sound is playing through the correct speaker side. It will say Left when playing through your left speakers and Right when playing through your right speakers.
You could put this onto CD too, to ensure your CD is playing the correct side still.
Here's the file:
Right click and save as Link