1. Use a tape adapter
2. You can use an FM modulator (Plugs into your aerial(antenna) socket, and enables you to set a frequency to tune into to hear the sound)
3. You can use the Aux. input on your head unit (If it has one)
4. You can use an Aux. input adapter i.e. CD-RB20 adapter for Pioneer decks.
5. You can run the input into an amplifier and bypass the Head unit all together.