Cassette Deck

… why would you do such a thing?

 

a hardwired install is very unlikely, you could run it through one of the usb ports or blue tooth it

 

If you are serious why not try something like this:

HDE Handheld Portable USB 2.0 Cassette Tape Deck to MP3 Digital Converter with

And just convert your cassette's to .MP3's and play them through the USB Port.

 

Or, just convert your Model S into a DeLorean:

TesLorean – DeLorean Electric Conversion Blog

...and then the car will come with a cassette deck standard.