I was having trouble getting my Wii Classic Controller successfully recognized as a USB joystick and I finally got it working (mostly). I had alot of trouble finding reference for the wiring on the controller itself so I decided to post here in case someone else has the same difficulties. I'm cheap and did not want to buy the WiiChuck adapter since I am going to be opening up the controller anyways and cramming the Arduino inside hopefully. Most Instructables or Tutorials I found were oriented around Assembly instead of the Arduino IDE. I used the WiiClassic library updated for Arduino 1.0 found on this site.
Credit goes out to This Page Here (http://www.imaginaryindustries.com/blog/?p=80) for doing all the heavy lifting. I copied the USBAPI & HID files into my core folder and then pushed the Wii button presses and joystick movement into the Joystick class in my Arduino sketch. As of right now in my sketch, the Dpad is bound to the joystick and the left and right sticks are emulating 8 pos hat switches. I'm only using 4 positions at the moment because I am lazy.
Below is a photo of my connections and two sketches. One is my functioning sketch, the other is a template with all the button functions for checking the controllers button status and X+Y positioning of the sticks. The wire color is as follows
RED - 3.3v
WHITE - Ground
YELLOW - SDA
GREEN - SCL