Chosen Solution
So I recently bought an iPhone 6s plus screen and I’ve hooked everything up myself it wasn’t my first time either. As I began charging it the battery logo shows and when it turns on the phone is pitch black I still can get notifications but can’t see anything. There are times that the screen will flick on then quickly off. So the only thing I can see on the phone is the battery/charging screen. No apple logo or anything.
Probably a defective screen, if the old screen still works, hook that one up and see if it displays properly on there.
Check the backlight capacitors above the screens flex cables connector (on motherboard) , seen many 6s plus with bad ones there. But on that model there is two backlights (one for left and one for right side) so should work if not both is bad. Still worth to check
