MacBook Pro A1502 2015-2016 Trackpad and keyboard not working repair

Problem description
Frequent Trackpad Cable Failures Causing Keyboard and Trackpad Dysfunction in 820-4924 Board on MacBook Pro A1502 2015-2016

Symptoms

 * Keyboard not working.
 * Trackpad not working.

Solution
Bad trackpad cable. This dies all the time.

On this year/model with 820-4924 board:


 * 1) Keyboard signal goes to logic board.
 * 2) Keyboard signal goes from logic board to trackpad.
 * 3) Keyboard/trackpad signal is turned into a SPI or USB signal ON THE TRACKPAD, and then goes straight to the CPU from the trackpad cable.

The trackpad cable going bad will stop the keyboard and the trackpad from working. However, the keyboard power button will still function since this works separately.