My dad's 1996 trooper's CD player continues reading the CD when the volume is off and even when the car is not running(turn off the radio and the car, and when it's turned back on, the track has progressed like it was on the entire time). It is causing a parasitic loss, so we are disconnecting the battery whenever the car is off for more than 20 minutes. what should i be doing to try to isolate the problem?