The music switch in the car is a button with music symbols or MP3. On the display screen of the center console, for cars without a center console display, the music switch is the CD or FM button. You can put in a CD or turn on the radio to play music. In most cases, the button with the word FM refers to the FM radio, which is the signal the car receives through the antenna. It's a ROM disc. Press this button to switch to disc playback. RPT is a loop playback. Press continuously to toggle between a single loop and an entire disc loop. CD refers to choosing a CD player that can play music from CDs.