It isn't telling you to use the same wire for two different things. It is telling you what wires correspond with which wiring.
You would match up the 12V constant for the factory to the 12V constant for the aftermarket unit....and so on.....
Example.....
Car Radio Battery Constant 12v+ Wire: Orange TO Yellow 12V Constant / Memory
1. So First you would wire the Orange from your factory wiring to the Yellow on your aftermarket radio wiring.
You are making this way more difficult than it has to be.
Example Two
2. Car Radio Accessory Switched 12v+ Wire: Yellow TO Red Switch / Accessory
So you would wire the yellow wire from your factory wiring to the Red "ignition/Switched 12V" on your aftermarket Head Unit Wiring.
If that doesn't make sense I really don't know how else to explain this to you
I can even see in the picture you posted that the colors seem to be correct.
Also make sure your vehicle is off and if things dont work when you turn the car on try hitting the power button on the radio or checking your ACC fuse for the car.
I get what you're saying. I DID do it just how your diagram showed, but it was slightly confusing. I will post you the exact order in which I connected the wires and what wires I got confused with.
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Brown
Car Stereo Dimmer Wire: Gray
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue
Common aftermarket Wiring Colors
Yellow 12V Constant / Memory
Red Switch / Accessory
Black Ground
Blue Antenna Remote
Blue with White Stripe Amplifier Remote Turn-on
Orange with White Stripe Dash Light Dimmer/Illumination
Green Left Rear Speaker (+)
Green with Black Stripe Left Rear Speaker (-)
White Left Front Speaker (+)
White with Black Stripe Left Front Speaker (-)
Purple Right Rear Speaker (+)
Purple with Black Stripe Right Rear Speaker (-)
Gray Right Front Speaker (+)
Gray with Black Stripe Right Front Speaker (-)
*Stock =(s) Aftermarket=(a)
Car radio battery constant. Orange(s)+yellow(a)
Car radio accessory. yellow(s)+red(a)
(Which yellow wire? There are two.)
Car radio wire. black(s)+black.(a)
(Does this mean I cut off the spade terminal on the aftermarket stereo to do it?)
Car illumination/dimmer: Brown(s)+orange(a) with white stripe
Car Dimmer. Gray (s)
(Do I connect all three brown orange with white stripe and gray wires together?)
Left front speaker positive. White(a)+tan(s)
Left front speaker negative. White with black stripe(a)+gray(s)
(Wait so the same gray wire as the car dimmer wire? There is only one gray wire.)
Right front speaker positive. Light green(s)+gray(a)
Right front speaker negative Dark green(s)+gray with black stripe(a)
Left Rear speaker postive Brown(s)+green(a)
(The same wire that is used for car illumination? There is only one brown wire.)
Left rear speaker negative green with black stripe(a)+yellow(s)
(Again which yellow wire do I use? There are two.)
Right rear speaker positive Dark blue(s)+purple(a)
(Which dark blue wire? There are three.)
Right rear speaker negative Light blue(s)+purple with black stripe(a)
Can you see why I'm having a hard time? //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif