The Nunchuck has an X/Y joystick, an X/Y/Z accelerometer, and two buttons (Z and C).
The sensor data is communicated through the i2c bus.
The connector contains four wires, two of which are power and ground. The other wires are used for i2c communication (SDA and SCL). The following diagram demonstrates the principle:
If you are worried about your connection, you can find an adapter for this controller at https://www.sparkfun.com/products/9281.
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