for those experiencing this issue, but have not achieved resolution: i just took in a 2012 MacBook pro retina 13 which had no display. after trying all of the suggestions, i ended up with a working backlight but no LCD. the solution was to disassemble the laptop and remove the LCD, then remove the clutch cover from the LCD. here i disconnected and reseated all connectors, and partially reassembled the laptop to test. ALL SYSTEMS GO. I suspect this computer took a fall also
allow me to answer my own question(s): if the trackpad doesn’t click, then the trackpad doesn’t click. throw parts at it. if the keyboard and trackpad aren’t working, fully assemble your machine, or at the very least, check the ground circuit because it appears to be incomplete without the case screws in place.