Hard to say. At this point I would venture to guess there is something wrong with the radio head unit itself. That is the only logical variable in this equation. If it works in one mode, then a change is made on one component and the symptom appears, logic tells us we should start there. Quite honestly, unless you can find a used unit, supplies are quite scarce (and expensive) on these radios, so it is hard to just plug one in to test. Aftermarket radios are still easy to install on the older cars. The only problem is finding one that doesn't look like Las Vegas at night when it's on (and doesn't clash horribley with the interior of the car).