I installed a different system, so I am not speaking with any authority about what you installed. However, my experience and research at the time might help with some of your questions.
Firstly, I'm impressed that you got those air vents out without the
vent pulling tool! Brave, I wouldn't have tried without the tool.
I'll take a guess on your wiring questions. Please, experts out there, join in to correct me if I'm wrong!
1) red wire labeled ACC-OUT,
Usually red is power and ACC is accessory, so if you had some other device needing 12v of power (like, a dashcam or a radar detector or something?) this cable is probably just a power pass-through
2) green wire labeled DVR-PWR,
I think this is something I wanted on my unit, where you can use a DVR to record input from a front camera. My front camera is on all the time (just not displaying), so why not use it like a dashcam? I had hoped I could find some sort of DVR pass-thru to record the signal as it was coming in from the camera and going to the head unit
3) black wire labeled GND,
Ground if you need it. I needed it. The sound was all crackly and once I connected the ground to a good spot on the chassis the sound improved greatly.
4) pink wire labeled 360-DET,
I am assuming your unit can handle the input for the 360-degree camera system. Do you have that system in your car? You'd have cameras on your two rear view wing mirrors and elsewhere and the signals are processed using way-cool algorithms to simulate a "birds eye view" above your car. You'd probably know if you have it and if you do it looks like you'd have to hook that up for the signal to go to your new screen.
5) brown wire labeled CAM-PWR, 2 yellow female AUX cables labeled CAMERA and DVR-CVBS-IN,
This looks like your camera power (my system talks to the Mercedes and knows when I put it in reverse so it knows to display the camera input to the screen). The rear camera is then powered by the head unit and only turned on when Mercedes R tells it to turn on. The DVR-CVBS IN is most likely how you can use a dash cam as the front camera. In my system, the front camera displays to my screen for 5 seconds after a take it out of reverse. This is awesome for parallel parking. The manufacture of my unit told me that I can use a dash cam as the front camera input. But, alas, I already had installed a dedicated camera into the front grill.
7) a green male AUX cable labeled COAXIAL-OUT, and
Does your unit play videos (like for the kiddos?) if so, Coax is a likely cable input to go to those screens (like the kind people put in the back of the headrests)
8) 2 USB-2 female ports.
?? USB ports are usually always powered, but maybe this is also for software updates? They may have many uses (kinda puts the "universal" in "
Universal
Serial
Bus")
Now, my guesses on your other questions. Remember, I have a different unit but I did do a lot of research on all of these units before installing the one I did.
1) I cant find a way to access the NTG screen in order to be able to change the radio station. A station plays when I push radio, but I cannot change it nor do I know what station it is on because I don't have a way of seeing that.
This may be a stupid question, and my apologies if it is....but have you tried holding down the CLR button next to your control dial for the infotainment system for a long time (like 5 or 10 seconds)? On my system, that's how you toggle between the stock infotainment system and the new unit.
2) Radio volume and CarPay volume are drastically different! CarPlay volume is much lower and if I switch over to radio, it will BLAST loudly.
I have the same issue. I cannot remember what I did to make it better, but I still never thought the sound quality was as good through the unit so I usually use the stock radio input (MMI or Bluetooth) for music. I think there was a setting in the unit's settings menu for volume level?
3) Sometimes I get a screen that says "Benz Check Signal" when I go to the car icon (where I would have expected to find the NTG menu).
This sounds like something in the interface between NTG and new unit isn't as expected. In my unit there was something about the fiber optic cables that had to be moved, beyond just plugging in the passthru cable. Like, there's a pass-thru fiber optic cable from the old unit to the new but then there was also a fiber optic cable that actually had to get moved from one box to the other. Did you take pictures when you were doing it? Do you still have it apart so you can see all the cabling?
4) CarPlay takes a super long time to load. I wonder if I install an activated sim card, if that would change the load speed. The lag time is very bothersome and was really unexpected.
I would recommend just getting it its own SIM card. That was the main reason I was thinking of installing something like what you have (it's basically an android phone, not just an interface from your own phone). In retrospect, I wish I had done that. I do find CarPlay WIRED is much faster than when it tries to connect wirelessly, so I am using that. But, it takes long enough to load that if I"m just running down the street I don't even bother to launch it. Again, we have different units but I think using one that is programmed to function like its own phone, with its own operating system (like what you have) would have to work much faster than something just interfacing with an outside phone (like what I have). If you phone plan is one that can carry another line for little cost and share data, it seems like it would be worth the extra incremental cost.
5) I only have 3 icons showing on my screen per page. I believe I am supposed to have 5. Can't find a way to change that.
I cannot take any guess on this one! Again, maybe settings? Maybe it's not set for the size screen you have with it?
Did your unit have any dip switches which needed to be set? If so, have you double-checked that you set those correctly? That could be where the screen size is set (which might determine the number of menu items it displays.
Again, lots of guesses on my part, but maybe something can point you in a direction to get things working better for you!