Here is a few tips and links to help with your car audio systems.
Estimating your electrical current demands:
To calculate the current draw of your amplifier, multiply the number of channels by the RMS watts per channel (for multiple amps, add the current draw figures to arrive at a grand total). Double it. Finally, divide it by 13.8 (the average number of volts an alternator produces). The result is your systems approximate current draw in amperes.
Estimating your alternator's reserve current capacity:
Take your alternator's amp rating and multiply it by 40% (0.4). This will give you an idea of your electrical system's reserve capacity.
I.E say your alternator's amp rating is 90 amps; 90x40% = 36 amps left to power your sound system. If this is higer than your amplifiers current draw you're in good shape.
The Install Doctor - The Do-It-Yourself Car Stereo Installation Resource
good site for stereo wiring diagrams
Crutchfield: Car Stereo, Speakers, Home Theater, LCD TV, Digital Cameras
good site for buying car audio and detailed information about what fits your car.
good site for wiring diagrams, sub box building calculators
I will continue to post links as I find them also feel free to post any you may have. I hope this info helps.