I just got a reply from Metra about the 70-7901 wiring harness, here it is:

Shawn
No the 70-7901 harness will not work on 2001 or newer Mazda's. Mazda changed to a new harness just this year. We don't have the new harness yet. I don't know when we will have the new harness. We have not yet had a chance to change the Description on the 70-7901 package.
Let me know if you have any other questions.
Mike Brechue
Product Specialist
Metra Electronics

:crying: I really didn't want to have to cut wires, darnit!! I'm getting a head unit really soon, as soon as my security system is installed this Friday. Oh well, we'll see what happens.

you have a few choices, but here are my 2 suggestions:

1)
Almost any electronics supply store will have universal male and female plugs (connectors) If you really don't want to cut out your plug compltely, in which i don't blame you one bit, you can insert another connector. You still need to cut the factory wires, but once it's all done, you'll have both your aftermarket plugs (connectors) and retain your factory plug (connector).

I would separate them into power and speakers with 2 separate plugs (connectors).

2)
cut the OEM plug so that you still have a few inches of wire. Add the new male connector to the wires in the car, then add the new female connector to the OEM wires on the OEM plug. This just made the OEM plug removable :D Then, all you need is a second indentical female connector, to add your aftermarket radio connector. There, you just made a harness and connector for the P5 :bt:

This way all looks professional and still gives the appearance of a factory look.