Attach the four motor and sensor wires coming from the unit lid to the motherboard.

Fold the top down over the vacuum and snap it into place.

This step should not require many pounds of force. If something does not connect together properly, remove the top again and check that all of your previous steps were successful. I find that most difficulty was related to correctly seating the wheel wells and routing the wires to the top of the motherboard under the plastic tab on the right wheel.