I have this deck in my '91. The unit is stuck in what is called the "reverse mode" i have no idea why the hell you would want it to do it, but it will reset to this everytime the battery is disconnected. to turn it off...Hold down the #5 button(#5 or #3) i'm not completely sure. and turn the unit off by holding down the "source" button for 2 seconds. the unit will beep once telling you that you have exited "reverse mode". also, this has to be done while the ignition switch is on.
Good Luck...by the way, there is something in the manual about this...can't remember where though.