Requirement: an empty project must already be set up, and the library with ECAD objects has been imported.
Using the context menu of the empty project, select the menu item Add > ECAD > WiringDiagram. See figure:
The Finder dialog for wiring diagram classes appears. The desired objects can be located in the Finder and inserted:
Use the [Search] button to display the available wiring diagrams. Confirm your selection with [OK] to create a root of the ECAD discipline as well as an instance of the selected wiring diagram in the project.