1996 Explorer Ford/JBL System Help

[1996BLKBauer]

OK so I just bought a 1996 Ford Explorer with the Ford/JBL sound system. This system has no bass what so ever. I have a few questions. Is there just mids, and tweeters in the doors? Or does all the bass come from the subwoofer in the back. The sub in the back does not work at all, I am not sure why either. I would like to know how to get at the subwoofer, and amp to try and find out whats wrong. is there a thread about this? It also seems that the bass knob on the head unit makes no difference, so that is why I am thinking that the sub has all of the bass.

 

[1996BLKBauer]

So nobody else has ever had this problem? or does everybody come here and ask about it? I honestly think that a regular aftermarket stereo would be extremely hard to install in one of these, with the extra amp, and sup, and controls in the back, so I would like to get the stock radio working right again.
any help at all would be great, even just a link to a thread already about it. Kinda lost here, and really want to hear my stereo the way it is suppose to be.

 

[toypaseo]

Here is a MTX pdf showing how to remove the rear panel...

http://a248.e.akamai.net/pix.crutchfield.com/Manuals/236/236FEX1T45.PDF