speakers dont work

i have a 1993 400e with stock stereo and when in FM mode only the right side speakers work but when in AM mode all of the speakers work perfectly, i have checked the balance and fade and they are both in the middle. can anyone imageine what might have happened?

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).

would a head unit from another class mercedes work in my 400E if both cars were the same year?

As long as it is the same unit (basically as long as it looks the same as the one you have).

I know this is probably a stupid question and you already told answered me but im gonna ask anyway. would a stock head unit from a 1994 E420 work?

If it looks exactly the same as yours, it will work. If it looks different, examine the connecotrs on both. It should plug in if the connectors are the same. I haven't tried mixing radios from different years, so no personal experience.

Ok, Thank You.