http://www.installdr.com/Harnesses/Mazda-Wiring.pdf
That's the wire codes or whatever so you know which speaker wires are which and power wires.
or for $5 plus shipping you can just buy the harness and not cut your factory harness:
http://www.sounddomain.com/sku/SCOMA02B
I'd suggest buying the wiring harness but if you don't wanna then just go by the codes in the first link.
http://members.sounddomain.com/nekketsu