So you've got this great little MP3 player or Ipod, but your old-school car only has a CD changer? Sure you can get an FM modulator, but they don't work so great and are notorious for poor sound quality. I decided to leverage the CD player in my car to add a CD-quality auxiliary input for my MP3 player.
What you need:
-- Stock car stereo with a CD changer input
-- Basic Soldering Skills
-- Soldering Iron & Solder
-- Hand held Volt/Multimeter (to find right wires)
-- Small gauge speaker wire (anything around 18-14 gauge will work)
-- 2 panel mount 1/8" stereo phone jacks
($2.99 for 2 at Radio shack)
-- 1/8" stereo plug cable
($5.99 at Radio Shack)
-- Old pair of headphones (really just need the wire & 1/8" plug)
Essentially what you are doing is sending a pirated signal from the MP3 player onto the line that would normally be sending audio from the CD changer. In order to prevent a mixing of the audio from the changer & your new pirate Aux input, you have to play a special CD which contains tracks with perfect silence. It may sound complex, but is quite simple with some basic electronics/soldering skills.