Singer Quantumlock 14T957DC Detailed Threading Manual page 30

Slip the thread into the third slot closest to the take-up lever.
Slip thread through third slot on the right; next slip it in front of the thread guide
and then into the eye of the needle (E) on the right. Finally thread the tail of the
thread through the opening in the foot directly below the needle; pull thread
under the foot and to the back of the serger.