The general rule of thumb according to the wiki, you are supposed to group your joint to the part that moves, well I can tell you that doesn't always work.
If you downloaded the model I attached to my reply, you can go in there and see what is attached to what and how, if you click on the joint, be sure you click one of the edges of the joint not a face, you can see what is grouped to the joint.
Then you grab the joint connector and do the same, you can see what is connected to what. Again be sure to click an edge of the joint not a face, it just works better.
If I had the presence of mind, when I draw something, to record it, I would, but in reality I when I have an inspiration, I just go to work, I don't think of recording what I am doing.
I would have to do that on purpose, and plan it out.
But I will try to record a future project.