[danielshun]

there is a good production--XCarLink
this adapter makes iPod or MP3 as a CD changer, and play iPod
or MP3 through car
audio system, it does not use FM transmitter, but wire connection.
(Plug into the CD changer port of the Head Unit). Once it is equipped,
you can choose music of iPod or USB disk from the car stereo's buttons
or steering wheel controls,
For example,
1 choose playlist from iPod
2 Select songs by Next or Previous
3 Multi Play mode: Repeat, Random, Scan
4 Charge function

this kind of iPod car adapter is wonderful, it can make you control the iPod by the car audio such as the CD botton or even the steering wheel. its brand is XCarLink, and you can search it in google etc

I think it is useful. If anything what to know, you can ask me.