DIY aux input on Alpine car stereo (M-BUS) :: 01 Jan 2010

If anything in this article is unclear or confusing, please let me know in the comments and I’ll do my best to clarify.

Disclaimer: by following the instructions below, you may end up destroying your stereo, car, MP3 player, interpersonal relationships, and everything else you hold dear. I am not responsible for any of this. That being said, it worked fine for me.

This method will work on any Alpine stereos with an 8-pin M-BUS connector in the back. (The stereo I performed this on was an Alpine CDM-9821.) The connector itself should look something like this:


After some searching around, I located the functions of each pin on this connector at The pins of interest are the bottom three:

This corresponds perfectly with the contacts on a 3.5mm headphone plug:

So all that’s left to do is make an adapter between the two. I ordered these parts from Digi-Key: CP-1080-ND, AE9918-ND, and CP1-3513-ND.

Gather up some solder, a soldering iron, and wire. Make the following connections:

  1. “Audio Ground” pin from the M-BUS connector goes to the pin closest to the hole on the 3.5mm audio jack
  2. “Right Audio Input” goes to the pin farthest from the hole
  3. “Left Audio Input” goes to the only remaining pin.

You should end up with an adapter cable like this:

Plug the M-BUS connector into the back of your stereo and mount the audio jack somewhere on the dash.

Now turn on your car. If all went well, nothing will start on fire. Hold the “Setup” button on the stereo and enable aux input in the menu. Now hit the “Source” button until you get to AUX. At this point, you should be able to plug in an MP3 player and have the audio routed to your car’s speakers.