Thank you for the awesome response Joe. I do not know if I have the factory amp under the seat, if I have the disc changer, surely I must then. I don't know how I'm going to make the blue/white amp cord from the harness stretch to fit to the amp, I will just have to splice some more wire in. The only blue and white I have from my HU, is the Auto Antenna, there is no blue/white amp wire that I can see, although it may just be a different color. I do have a blue and white coming from my wiring harness though. I'm pretty sure I'm using that model Metra harness, I put a photo up showing the exct wires I have from my harness. They did have RCA inputs on the harness to wire in the speakers, although as I did not have a clue where they go other than just for splicing in the +/- of each speaker, I cut the RCA ends off, and wired them to the audio out's on the HU. I have seen and read that grounding out the parking brake (-) will fix the problem of video not always playing, I have read that I can literally ground it out anywhere and showed that it will work too, is this true? I still have zero power, I am doing this for a lady though and I haven't been back until I hopefully got a full walkthrough on the site here. Your response was awesome Joe, thank you for that. I have wired tons of vehicles but none have ever been this complicated. There is no back up camera to worry about, I just didn't know if I needed to do something with that wire. Look at my photos, I know I have a Metra harness, but whether or not it's the exact one you're talking about idk. Thanks again for all the help

 

Your OEM harness should have key powered 12v and always on 12v. If these are not hooked up right, your HU will not retain any settings, and you will have to manually turn it off everytime you turn off your truck.
Your pic of the wiring diagram of the boss, does show you have a yellow and red wire to be hooked up to switched and unswitched power.
Red is switched and yellow is constant power. make sure this is how it is hooked up.
If you are not getting power, to these OEM wires, check your fuses under the hood and under the steering wheel.

 

You do not have to have the blue/white wire go all the way to the amp, there is a wire on your OEM harness that goes to your amp. I will have to look up the OEM wire colors and will get back to ya. That blue/white antenna wire IS the amp wire. and it need to go to the corresponding wire in your harness, do not splice anything yet.

 

Your RCA wires, that you cut off were for the RCA output from your HU to your OEM amp.
The speaker level wires you hooked up will more than likely be more than your OEM amp can handle and sound will be distorted.
If you did not have the OEM amp then those speaker wires would go straight to your speakers. Most HU have both line level and speaker level outputs. one for amps, the other for speakers.
If you can, rewire the RCA plugs back where they were and hook up to the corresponding RCA coming out of your HU.

 

If you just feel under your drivers seat, you should be able to feel the cooling fins on the amp.

 

This will help you with the OEM wiring harness.
2003-2004 Land Rover Discovery with Alpine Wiring Information

 

I literally responded a whole book already, but idk where it went/what happened to it. I do not have a rear camera to worry about, I don't know whether or not I have the factory amp, although it does have the changer, so I assume it has the amp too. I have a blue and white coming from my harness, but I don't have a blue and white coming from my HU other than the "auto antennae" wire. I have included much better photos on my last post that are a little easier to see. So I have to run the amp wire all the way from the harness to underneath the seat? And the speakers wire in there too you say? I have no clue how they are meant to reach, unless I cut into them and splice more wire in, (which i have already cut the RCA leads off of the harness, to directly connect the +/- for each speaker on the back of the HU). The pictures of the back of my HU, is the best way to describe all the connections I have, and be super specific in your responses please. It helps me tremendously. The picture of my harness, I managed to get every wire in that photo as well that it has on it. Thank you all for the help!

 

Ok, Your OEM harness has the wires and the amp turn on wire. The link i posted shows the OEM harness and wire colors. You do not have to run anything from your HU all the way to your amp, they are already there.
The red/blue wire on your harness hooks up to the blue/white wire on your HU, This turns on your amp and antenna booster.
Your OEM amp takes the 4 speaker inputs and sends the sub signal to the subs, without you having to hook up separately.
If you go to the link, only look at the HU wiring, and disregard the amp wiring(you will not need to mess with them)
I looked at your pic of the boss wiring schematic on your earlier post and you should be able to match up all the correct wires to the corresponding wires on the HU.

 

So if I'm reading this correctly, I take the red(the hot) and the blue (Amp wire I believe it is?) from my harness, and wire both of those to the blue/white on the HU, the Auto Antenna? Rewire the RCA outs I cut off to rig up the +/- of each speaker on the back of the HU, then plug those RCA out's to the RCA IN's also on the back of the HU? Thank you all for the help seriously. Like the easiest and most descriptive way of how to wire this damn thing with the stuff that I have, wins. lol. You can not be too descriptive. Thanks again for the responses

 

You will take the red wire from the HU and hook it up to the light green/violet on the OEM harness.
You will take the yellow wire from the HU and hook it up to the violet wire on the OEM harness.
You will take the blue/white wire from the HU and hook it up to the red/blue wire from the OEM harness.
When i say the red/blue wire I mean it is red with blue stripe, light green/violet means light green with violet stripe, blue/white means blue with white stripe, red/blue means red with blue stripe.
You will never hook up two wires from HU to 1 from harness or vice/versa.
When and if you install the micro bypass, or the steering wheel control, you will have a couple of grounds together and maybe a couple of hot wires together, but that is the only time you will have more than one on one wiring.
Yes rewire the RCA plugs and plug to corresponding outputs on the HU. You will not hook up the the RCA plugs on the HU that are marked input, or the yellow ones called video output. they are only if you are installing an auxiliary device(in the case of the red/yellow/white that are marked input) or an external monitor(yellow RCA marked video output).
You will not have anything on the sub RCA output, unless you are adding an additional amp and sub-woofer.