cuckoo & door staying open?

i have an old German, 8-day Schatz cuckoo clock. i recently replaced the bellows-tops material. I think i did everything right. But... now, when i attach the left-side weight (looking from front), the door opens and stays open. (i have ckecked the little wire that lifts the cuckoo, it is positioned under the tail). - i am now noticing that there is a thread of some kind on the left side of the inside (looking from the back). it is attached on one end to a metal hook/loop, but the other end is loose & looks frayed/broken. if i tug on it, some parts of the mechanism move. What is this thread for, and could it be my problem?? and is it fixable by a non-professional clock-fixer??