If there were no issues with the soldering connection in Step 6, check the wiring in the picture shown.

Remove the zip ties with a pair of scissors. Then remove the plastic that covers the wires.

If the wires underneath the plastic covers are loose or disconnected, try to desolder and solder the wires. Use the iFixit soldering guide to assist in this step.

Soldering iron is very hot, use caution when handling