The old stock stereos are junk. Back in the late 1990's, when I worked at a Chrysler dealer, I was changing stereos that were only 3-6 months old that just died! Best thing would be to replace the stereo. If you do, get the faceplate adapter, and the aftermarket wiring harness adapter. Both of these are fairly cheap, unless you go to a Stereo shop. Go to WALMART! You would be suprized at what they carry. You can check a speaker for power by simply using a small ( AA,C,D,9V) battery. Just touch the speakers wires to the ends of the battery momentarily. You should here a "static" type noise, and the speaker should move slightly. Remember, the speaker should move outward. This is how using the battery (preffer 9V- more power) can tell you which wire is possitive and negative. Don't be affraid to install this yourself. If you need new door speakers, they are 6"x9". If you get speakers that have other speakers sticking out the top ( ex: 3 ways ), you will have to mod the door panels.
Here is a wiring diagram. Hope some of this helps: