How about a viewing mode where the source and potential destination modules are displayed bigger - the modules would be the one you clicked to start the cable and the one the mouse is currently over. That would make it easier to connect the cable.
Here is a poor mock-up:

Also, such a mode would be handy when adjusting the module controls. You have the overall view of the build, but it becomes easier to twiddle the controls. Having to zoom in and out and scroll around is annoying.