So, that's what why my Ruby console tell me (me):
(pressing joint select button)
onSelectionCleared
Inspecting model for errors
(selecting hinge)
onSelectionCleared
onSelectionAdded
onSelectionBulkChange1
Webdialog set to#Sketchup::Group:0x6962588
(selecting box with left ctrl-button)
onSelectionCleared
onSelectionAdded
onSelectionBulkChange1
Webdialog set to#Sketchup::Group:0x684afd0
Hmmmm! There is no onSelectJointConnecting or something like that.
Hello!
As a native german speaker from Dortmund in western part of Germany, i try to remember my good old school english 
So please be lenient toward me.
I hope, this is only a newbie question.
I've installed Sketchup Ver.7.1.6860 with Sketchyphysics 3.
When i try to connect a hinge (grouped with a cylinder) with a box via joint connect, the two parts are still disconnected.
And yes, i press the left ctrl-button (and the right ctrl- and the left alt- and the shift-button and...) to select the second part.
In a drawing from google warehouse are some tyres connected to a body. If i open the Sketchyphysics inspector, i see how parts are normally connected.
But not in my drawing (see attachement).
So, do you know how to connect the two parts?
With best regards
Mathias