Threading diagram needed for the looping needles

There are quite a few pictures of threading diagrams on the internet. Just perform a search for the make + model + the word "threading."

Be sure to follow the threading order specified in your owner's manual. If the order is not followed accurately, the machine will most likely not work properly. Also, be sure to RAISE the presser foot BEFORE threading. While threading each thread, grasp the thread with one hand between the thread tree and the tension disk and grasp the thread below the tension disk with the other hand and gently tug the thread to make sure it has seated in the tension disk. With most sergers, the lower looper thread MUST drape over the top of the upper looper in its final threading process Before being pulled under the presser foot.

Juki MO 816 threading Google Search

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiOt_7mqbHKAhVK52MKHc5XB5MQFggdMAA&url=http%3A%2F%2Fwww.raichert.com%2Fadobe%2FMO804-12-16%2520Inst.pdf&usg=AFQjCNH1vfonoEQ29McTsOItvQoW8ECZag&cad=rja

If any either looper thread breaks or comes unthreaded, it is the best advice to unthread all the looper threads and re-thread from the BEGINNING. Just bite the bullet and do it. It will save a lot of frustration.