The trackpad cable is a dual use! It connects to both the trackpad as well as the keyboard. Make sure the connection is not damaged on the logic board.
In this series there is also a mid board just above the trackpad which you can see in Steps 8~10 in this guide [guide|142682] see if there is any staining or corrosion on it as oftentimes that is the problem. You should review the connections as well making sure the ribbon was fully and squarely inserted before the clamp latch was engaged.