The wires have both a female and male connection. You simply need to connect these until they have clipped into place.
Please ensure you check the wires whilst you are assembling the treadmill. If the wires have been squeezed, dented or pushed together it could affect the performance of the machine. If you are experiencing difficulties with the connections then we advise you to check the male pins to ensure they are all straight, if one is out of line it could prevent the clip from forming a solid connection.