I tested all the speaker output wires from the headunit with a battery. This is the standard 4 speaker headunit. Not cd-changer, I don't know if the cd-changer has a different output, I would assume not.
This is the example of the stock p5 head unit
The pin 9-13 are different, with a few more added in, I did not test those.
1-8 are the speakers
Pin 1&2
Right Front white/black -
Right Front grey/black +
Pin 3&4
Left Front white/red -
Left Front grey/red +
Pin 5&6
Left Rear white/purple -
Left Rear white/grey +
Pin 7&8
Right Rear white -
Right Rear grey +
The positive/negatives are educated guesses using similar mazda wiring harness diagrams. I assume these to be correct. I did not test to see if the speaker cone moved forward or away like crutchfield says to do though. They sound fine to me the way its wired, so I don't know what the difference is if the polarity is reversed.
Also, I have not tested an aftermarket wiring harness, but the channel outputs are different than say, a Protege 5. So if there is a "standard" Mazda wiring harness that supposedly covers X through X model years, the channel outputs would be incorrect. For example, the standard pin-out for a Protege 5 pin 1 & 2 is Right Rear, but on the CX-7 pin 1 & 2 is Right Front.