From: 1957 Dodge Owner's Manual:
Here's a marvel of the electronic age. The new Dodge Highway Hi-Fi Record Player (optional equipment) provides your favorite music wherever you drive... whenever you want it. The unit utilizes the car radio speaker and volume and tone controls of the Touch-Tune Radio. (This model of radio is required for Highway Hi-Fi operation.) If a rear speaker is installed, both the car radio and Dodge Highway Hi-Fi Record Player use the same rear seat volume control. An ON/OFF switch on the player cuts it in or out from the radio speaker.
To operate the Dodge Highway Hi-Fi Record Player, follow these five simple steps:
1. Unlock the cabinet door by inserting key and turning all of the way to the right, then pushing in on key and lock button. (If you wish, leave door unlocked and merely press lock button to open - snap shut to close.)
2. Pull turntable out by handle.
3. Select desired record from record storage space directly beneath turntable and place it on turntable.
4. Place needle on outside edge of record, and move switch lever to ON position. Slide turntable in and close door.
5. Set tone and volume controls on radio dial as desired.
Your Dodge dealer will give you a listing of record titles, and he will gladly tell you where they can be conveniently purchased.