joints - where are the connection points?

i hope i haven't missed this in some documentation. if i create a joint, i.e. a ball-socket-joint, at wich points does it connect the two bodies? can i somehow make joints visible (for debugging purposes)?

i experimented with a hinge joint and is has a very strange behaviour. i have created three box-bodies. the one in the middle is hinge-parent to both outer ones. as pin i used the Z axis, like this:
Z
/\
|
|. OOO
+-OOO->X
|. OOO

but not only the outer ones can tilt around the X axis: if the whole things falls off the terrain (the simple one from the tutorials) it seems like they have NO restriction in movement and everything falls apart.

when i try this in the NewtonPlayground it works like expected. do i need something special?

did i forget something? are there any typical mistakes i could have made if joints doesn't work like expected?

and the joint connection points, i only can think of the position vector of the body oder the center of mass. are the newton bodies created around the given position vector or positioned at the vector, so one corner of the box at it?