A:Answer You have to buy two or three addl relatively inexpensive pieces, depending on your car:
* a wiring harness that is specific to your car and to the new radio. You will unplug the wiring connector that goes to your old radio and plug that wiring connector into one end of this wiring harness piece. The other end of the wiring harness piece plugs into your new radio.
* an "installation kit" thing which is really some plastic and/or metal cutouts that fit the dash area of your car. These pieces allow your new radio to fit in securely to your dash and, again, are specific to the new radio model and your car model.
* I did not need an antenna adapter, but apparently it is sometimes necessary to allow your existing antenna wire (that you remove from your old radio) to plug into the new radio. On mine, it was the same connector so no need for this part.
In short, the "additional hardware" refers to some bits that are specific to car make and model, so they cannot practically include these pieces in the box of the new radio since they don't know what kind of car you have!
