I had the 2 front door speaker of my 2008 4 dr laramie go, the sound system was infintiy. They provide all the low end for the system. These were not the kind with the amp built in as the amp was located behind the glove box in a really hard to access place. After much searching and finally having taken my entire dash apart to look for loose wires i discovered why both speakers stopped working. There is a very finely braided copper wire that connects the voice coil of the speaker that comes through the cone and connects to the bracket that you plug the speaker wire into. Although at first sight it might seem to be soldered and connected to the back of the receptacle but if you very carefully wiggle the copper wire while the stereo is on a med volume the speaker will kick in and out. Atleast they did for me. So im very carefully resoldering the end of this finely braided wire to the point where it was hanging on after have cleaned everything ofcourse. It seems that moisture is the culprit here which caused the copper wire to corrode in both doors. I tested both speaker connectors coming out of the door to visually see that current was infact being sent to the speaker. I could just replace the speaker but im cheap. Besides we throw too much away today without actaully trying to fix it.

 

I have a 94 RAM van with Infinity sound system and yes, the amps are built into the doors right behind the speakers.