The VW-01B is the plug you wire to the back of the head unit and plug into the factory harness plug.

You may need a Euro-to-US radio antenna adapter too - depends on the head unit.

The harness is going to have a reverse signal and speed signal because of your nav system. You will need to check to see if your head unit takes those inputs from the same pins or not.

If not you would want to connect the wires to correctly capture those signals or if the head unit does not use them, leave those wires from the VW-01B disconnected and taped over.

You may also want to check the phone mute lead spec and accomodate that accordingly.

The factory amp will continue to work. One thing you will find is that the head unit "rear" control will do nothing. That's because the rear speakers in the Crossfire are connected to the "front" leads at the back of the radio and get sorted inside the amp. I used the "rear" channels from the head unit directly out of the head unit wires and routed my own wires to additional rear speakers. It works very well.

Check also the wiring for the red and yellow wires (accessory and battery 12v respectively). You may have to check those leads on the car harness to make sure you connect them correctly when you wire the VW-01B to the head unit.

Make sure to get the trans-thermal, polar-shifting, parallel neutralizing graphite injection system - Best Buy will cut you a great discount if you buy it when you get the head unit but charges at least double later....