Short answer....Lack of power for the speakers.....as for the wiring....here's the link:

http://www.fjccentral.com/tech/Audio_Wiring.pdf

Brimman should be in to give you the long answer soon.....

 

even if you had a wire switched, you will notice a lack of bass, not distortion. homeboy nailed it. lack of power. you are pushing your system past its capabilites. the amplifier in your stock headunit is being push beyond a clean signal. thats as long as i really want to go unless you are dying to know more. let me know if you have any further questions or problems.

 

Great guys! thanks a lot, not I get to tell my wife I'm going for an amp or new deck

I checked the web and it said the same thing but you guys got me first.

Underpowered system which I hear is worse than overpowering your system.

 

with stuff like you are running now, it just sounds bad. when you start reaching a speakers limits heat and power wise, clipping a signal can do major damage. i run 2200 watts rms on a pair of woofers that calls for 400-500 rms each, no issues. and i absolutely rail on them. i ran a pair of 500 watt amps on a pair of woofers that called for 750 rms each (in a sealed box, not nearly as tempermental distortion wise) and i killed so many pairs.

underpowering generally ends up clipping the signal because you arent getting the performance you want so you push it harder, past its limits.

i can still force my high end alpine and zapco EQ to clip.