Searching for a new head unit last night with an aux plug for my MP3 player I found an adapter plug for Pioneer head units. It plugs into the socket for the cd changer on the back of the HU. The plugs cost $35!!! Searching around for a cheaper adapter plug I found a sight that had instructions on how to make one and it even had the pin out for the HU. This only works on the Pioneers that control an externall cd changer, but I'm sure if you have another brand with that function you can make one too if you get the pin out for your HU.
I made mine this afternoon in about 5-10 minutes with parts I had at the house. It works GREAT. Now I don't have to pack around all the cd cases in the back seat anymore.
Here's the link: MP3 adapter

