Ah, you didn't tell me it used to work. If it has a new head unit I would for sure guess the dealer did not hook it back up properly. There should be a red & white plug that goes from the TV OUT on the Jensen that in turns goes to an Audio IN on the Magnadyne.
You'll also have another red/white/yellow that comes out of the Magnadyne and into AV1 on the Jensen or the switch box depending on what you have.
PLEASE do not send questions via Private Message, my inbox fills up too quickly. Post questions in the forum as a new thread so that other users can benefit from the answers. Use Private Messages for sensitive information only (VIN, Contact info or things you do not want the public to see).