Don't buy an FM modulator at Radio Shack, they'll sell you an FM transmitter (not the same thing). What you need is a device that has an RCA input, and goes plugs into the antenna plug on the deck. The factory antenna then plugs into the modulator. This allows you to use the input on the device with a dvd player or a game system or what have you by tuning the radio on FM to whatever the device is set to, usually in the high 80MHz range, depending on the unit and it's configuration. You can get such a unit at any car stereo shop, or Walmart.