In my harness I have 15 wires with only one of them being a true yellow. **EDIT**I have 3 dark green wires, one bigger gauge wire and 2 smaller ones. The green ones were the only ones im not sure of. As for the yellow wire I have voltage at the fuse block but not at the harness end. Yes I did swap in a fresh harness end. Im kinda stumped
**EDIT**

 

Battery
ORANGE
(+)
RADIO HARNESS

Accesory
DARK GREEN
(+)
RADIO HARNESS

Ground
BLACK
(-)
RADIO HARNESS

Illumination
GRAY
(+)
RADIO HARNESS

Dimmer
VIOLET/WHITE
(-)
RADIO HARNESS

LF Speaker (+)
TAN

LF Speaker (-)
GRAY

RF Speaker (+)
LIGHT GREEN

RF Speaker (-)
DARK GREEN

LR Speaker (+)
BROWN

LR Speaker (-)
YELLOW

RR Speaker (+)
DARK BLUE

RR Speaker (-)
LIGHT BLUE

That's your wiring. but if you really want you can clip off the yellow from where you have it hooked currently and hook it to the orange accessory wire in your ignition wiring. fuse it obviously. you should turn on from there. meter that "other yellow" and see to be 100% you didn't get them mixed up.

 

Here is a pic of my new harness end. The harness in the blazer is identical. The yellow is the only actual yellow wire. There is one that would resemble a "dirty" yellow but every wire is color matched. Im about to tear my dash out and trace the wire from the fuse block to the harness end.
Question, if I take the yellow wire from the harness end and tie it into the orange constant wire so both wires will be constant to the HU, would it hurt anything?

 

I think your just dumb. roseburgians... they struggle a bit

 

Oh i forgot to tell you, i did get my stock stereo workin, turns out I did pop the lil 10A fuse in the inside panel. lower left corner. dangit

 

brad your just jealous because I live in lost wages and you dont so suck it!
I have checked both fuses, both are still good. I just tried to tie the yellow and orange together on the harness end and connected them to the orange coming from the dash, still same scenario. Now my ****ty battery is dead so its on pause for now.

 

From that picture i'm looking at that yellow that looks real yellow is your left rear speaker wire. i have a metra harness in front of me for a gm and that's waht it's pinned as from waht i can see.
the switched 12volts will be RIGHT NEXT TO THE CONSTANT 12v. exactly next to it.

 

The wire directly next to the constant is a dark green wire. Also I color matched the wires. Would there be a difference because my blazer is a 99 and the HU is from a 00?

 

Color wise there may be a difference. but pin location wouldn't change. since gm used this harness from like 88 til about 02ish. as a matter of fact i recall seeinga green switched wire from time to time. but whatever is next to your constant is definitely supposed to be your switched wire.

 

When I get back I will try and swap some of the wires, thanks for your help!