I doubt its the Jensen. There was another brand back then that was used a lot, but I can't recall the name. In any case, I think its too old to spend a lot of time troubleshooting. You can get far better quality with a $100 head unit for a car. Another $30 for the mounting kit and you'll be all set.
2013 Jayco Jayfeather X20 E, 2008 GMC Sierra 1500 Crew Cab Z71 SLE