Car Stereos: 1996 pathfinder, farad capacitor, nissan pathfinder

Question
is there a special way to connect an aftermarket amplifier up in a 1996 nissan pathfinder LE. I have hooked up 20-25 systems in my life and never had this difficulty.  the amp is a Rockford power 500 bout 10 years old. worked fine in car i took it out oflast week. after hooking it into the pathfinder i just bought, it doesnt seem to put out proper power. to get any knock out of it i need to use the bass boost dial up all the way and still it doesnt sound like it used to. i tried using a compriable amp that belongs to my cousin, and i got the same result.  My wiring seems correct but i am starting to pull my hair out. the ground appears to be strong and i am also using a 1 farad capacitor.... please help.
thank you

Answer
Vinny,

There are only a couple of things that come to mind.  First, if the subs are wired up opposite of the door speakers (reverse polarity), the bass will be reduced significantly.  So, I would switch the incoming speaker leads negative to positive.  See if that makes the difference.  Second, Be sure the leads going to the subs are wired correctly.  If there is some sort of change in the wiring, it may be causing the problem.  Sometimes, people rewire the subs, so there is only one sub instead of two, or there is two instead one, or they are bridged instead of not bridged, etc.  All of these changes change the output of the subs.  Also, if you are using two subs, one sub may be wired opposite the other sub (reverse polarity) causing the lack of bass.  So, if the first reversal doesn't change the sound positively, then I would switch wires on one of the subs.  The sound difference should be very noticeable.  Hope this helps, Scott