While there are dual subwoofers back there (assuming a convertible, coupes got a single larger sub in the rear center) the fade should fade the sound to the rear speakers and not to the subwoofers. This sounds to me like there is definitely a problem.

 

Andy, play with the fader and balance controls at the same time. Isolate the sound to a single corner of the vehicle (ie, fader to only the rear, the balance knob to full right). Do you get the full range of sound? If no, then you most likely have a bad speaker (check below for proving the speaker bad). Now, move the balance to full left. Do you hear the full range of sound? If yes and it sounds like the right rear speaker, then you may simply have older speakers and they are not producing sound like they were when new. If no, then odds are you have bad speaker(s) and they need to get replaced. But, before you replace speakers, we need to verify that you don't have another problem.

To prove the speaker bad, you first need to disconnect the plug on the speaker. Now, with the multimeter set to resistance, do a resistance check across the speaker in question and verify that you are getting around 4 ohms (should be around 3.9 ohms plus lead resistance, may be as high as 6 ohms depending on the version of speaker you have). If you are up over 10 ohms, then you have a bad speaker (or two). Next, with the stereo system on and up at half volume, set the multimeter to the ACV position (10 volt range) and connect your multimeter across the two pins of the plug running to the car. Are you getting over 3.0 VAC? If yes, then this verifies that the radio is outputting an adequate signal and proves the speaker bad. if you are not getting over 3.0 VAC, then you have either a bad wire or there is a problem with the radio.

Hope this helps. If you need more assistance, let me know.

 

Andy, you have 8 speakers in your car. Please keep in mind that you have a speaker in the fascia, aka dash (full range speaker), two in the door (one tweeter, one midbass), and a full range speaker in the rear.

As for locations, the fascia/dash speaker is down in the corner of the dash at the base of the A-pillar. This speaker is in a half moon opening. The tweeter in the door is mounted in the triangle piece in the bottom forward corner of the side window. The midbass speaker in the door is down in the bottom forward corner of the door. As for the rear speaker, if you sit in the rear seat, the speaker will be right about where you hip would contact the side of the car.

What I would tell you to do is dial the stereo system to each corner of the car and run your ear near each speaker and verify that they are working. If you have problems reaching the ones in the dash, use a cardboard tube like you have left over from a roll of paper towels to focus your listening through the tube.

Hopefully this gets you going on down the right road.

 

I know this is a late post, but I just joined !
The rear speakers (by your hips) ARE the subs in the convertible. So...technically, there aren't any full range speakers back there. Your sound comes from the Doors and Dash...except for the Sub by your butt.