Any Pioneer deck needs this interface. Your best bet is to get it from Crutchfield. That is where I got mine and it was the cheapest.

 

I have a Pioneer deck that i got installed at circuit city.
I was also confused as if i needed this 70$ accessory also, but i asked a few questions at a local car audio shop.. and he was like anyone that has enough experience to do it will get it done without that accessory. Then when i got my deck installed @ circuit city im sure he took power from the Cigarette lighter to power the deck. I did need the antenna adapter though. And for about 6months now ive only blown one fuse which controled the Windows and Deck and im sure the cig lighter also.