I just got my package with the set. I recall there was a step by step manual on how to install this with oics included. I remember it looked pretty easy and I've gotten so far as to removing the lower glove compartment. However, it doesn't look like getting to the back of the radio would be easy. Help is much appreciated.
Here's the installation guide that someone developed and posted on the site. I got my unit last night and just installed it today. It was pretty easy -- took about 20-30 minutes and works great. Good luck!
How To Install the VAIS AIC-100i iPod Adapter btw, This information is also available in the FAQ: Toyota Prius FAQ
