Amp Wiring!!

Quick question for anyone who can help........

I've got a 1996 Ford Explorer Ltd and just got a new head unit stereo for it. I got it installed by a third party, and when it was done, the subwoofer in the back didn't work. After trying extensively with no diagrams to the vehicle, I thought this would be the best way. Does anyone have amp and speaker diagrams? Do all the speaker wires go through that amp? And how do you get the qtr panel off to get to it??

Sorry for asking more than just a quick one!!!

Im good with speakers. And my advice is if your running subwoofer than you want to by an amp for the sub not the the explorer has in it. You will definately get more power to the subs. Most likey why it didn't work when it was hooked up is because they probably didn't hook it up.
What you need to do is by an amp, easy to install just run a hot wire from the battery to your amp for power, then run your remote wire, and audio video wires from the back of the radio unit. and then run speaker wire from subwoofer to amp channel and then you got some killer bass. they have amp wirring kits .