Singer Quantumlock 14T957DC Detailed Threading Manual page 19

Using the tweezers thread the last thread guide that is located on the left just
below the looper. Next thread the brown looper eye from front to back, pulling
thread over the top of the red looper, then pull the thread tail to the back of the
serger 4 to 6 inches. Make sure the thread sits over the top of the "V" cut out
just before the eye of the looper. (See page 21 figure 10 of your manual.)
Tugging slightly on the thread tail at the back of the serger, push threader lever
all the way up to hook thread into the eye at the back of the looper.