There is a 4-pin Molex connector on back of the radio which must be connected to the original harness like below picture shown:

After that, the buttons from the steering wheel must be programmed.

You can study these buttons from System menu->Steering Wheel Control option.

Please press "Reset" twice before programming.

Then program each buttons, for example: click VOL+ on the radio and then press the VOL+ button on the steering wheel until you study all the buttons.