SuchTrk, I hope your project is progressing satisfactorily. So far I've obtained:
Amazon.com: Nexus 7 from Google (7-Inch, 32 GB, Black) by ASUS (2013) Tablet: Computers & Accessories
"Sponsored" Timur's Kernel
USB Host OTG cable + Charging
Double DIN install kit
Amazon.com : Metra 95-5812 Double DIN Installation Kit for Select 2004-up Ford Vehicles -Black : Vehicle Receiver Universal Mounting Kits : Car Electronics
5V DC regulater
Amazon.com: DROK® 10A/50W 9-32V 12V/24V to 5V Car DC Voltage Converter Regulator Power Supply,Waterproof: Electronics
The N7 is rooted and Temur's Kernel is installed; everything seems to be running fine.
A couple of confusing things:
1. The replacement 90* micro USB cable isn't listed as an OTG cable, but it seems to be doing the job.
2. The description on Amazon for the "Y" cable specifically states that it won't charge the tablet, but it is. ???
I connected the OTG "Y" cable in line with the standard N7 charger while watching the Power Event Manager. I enabled F1 mode, fast charging, and firm sleep. Show suspend screen... And show wake up toast were enabled by default.
External power and charging battery indicated correctly when the power cable was plugged into the female micro USB. The tablet shut down and came back to life when power was disconnected and reconnected.
Where did you find the 12V switched that stays hot while the key is in the "start" position? It doesn't appear that the 12V switched to the stock radio does.
I am currently using the one in the harness but sadly it does not stay on while cranking. I am currently on travel for work right now so I haven't been able to mess with it in a week or so. I apologize for the slow response
For charging with the Y cable it has to do mostly with software and the hardware in the tablet. If you were to uninstall Timur's kernel you wouldn't be able to charge at the same time. Due to how the stock software is designed. On stock otg I'd you plug in say a USB drive it will pull power from the tablet. Since the tablet is outputting power it can't charge. The kernal changes how that works. With their kenal installed and ( if I remember correctly) have fi mode enabled in PEM then if you just plug in the USB thumb drive it won't work till you plug in a power source. That is because the kernal stopes the tablet from putting out power so it can charge instead.