So I've found a 2003 radio wiring diagram for both the Base and Premium audio systems and I have a few questions.
I am going to be installing a line out converter, and a remote turn on lead.
I assume I have to take pry off the bezel, remove two to four screws, and tap the wires that are connected to the back of the factory radio which has a twenty two pin harness. I also need to tap a remote turn on lead, there is no specific remote turn on lead like the Premium audio system has so I assume I'll need to use the Fused IGN wire (Pin 2).
I don't know if there's a ton of room back there for the line out converter but there should be enough, and hopefully running the RCA wires won't be difficult.
This is the audio wiring diagram I'll be using:

Does all of that sound correct?
Wire Function Color Note Fuse # Size Location
+12V DC Battery(Constant) Pink 51 20 Amp Integrated power module on left front of engine compartment
Switched Accessory BROWN / red PTC 2 4.5 Amp Integrated power module on left front of engine compartment
Ground BLACK/ dk.green
Remote Turn On(output) Dk.GREEN/ red
Illumination ORANGE / dk.blue
Steering Wheel Control Wire Gray/white & black
Left Front + Dark green Line level output
Left Front - BROWN / red Line level output
Right Front + Violet Line level output
Right Front - Dk.blue/red Line level output
Left Rear + BROWN / yellow Line level output
Left Rear - BROWN / lt.blue Line level output
Right Rear + Dk.blue/white Line level output
Right Rear - Dk.blue/orange Line level output
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AMPLIFIER OUTPUTS
Wire Function Color Note Fuse # Size Location
12V DC Battery Violet 21 20 Amp Integrated power module on left front of engine compartment
Remote Turn On (input) Dk.GREEN/ red
Left Front Mid + Lt.GREEN/ red
Left Front Mid - Lt.GREEN/ dk.green
Left Front Tweeter + Yellow/black
Left Front Tweeter - Yellow/red
Right Front Mid + Lt.blue/violet
Right Front Mid - Lt.blue/black
Right Front Tweeter + ORANGE / black
Right Front Tweeter - ORANGE / red
Left Rear Mid + WHITE/ red
Left Rear Mid - WHITE/ black
Right Rear Mid + Tan/violet
Right Rear Mid - Tan/black
posted_image AT SPEAKERS
Wire Function Color Note
Right Front Mid + Lt.blue/red
Right Rear Mid + WHITE/ red
Right Rear Mid - WHITE/ black
Center Channel + ORANGE / black S 217 behind left side of dash (same line as right instrument panel speaker)
Center Channel - Yellow/red S 218 behind left side of dash (same line as left instrument panel speaker)
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An unused pin in the factory radio connector will have a +12v on with the radio power, you will need a skinny test lead on the DMM to verify this.