Use the Home > Select > Select > Coordinate Specification > Click Joint in YZ Plane command to select all objects on the specified plane.
Click the Home > Select > Select > Coordinate Specification > Click Joint in YZ Plane command.
Pick any point on the plane desired and all elements on that plane will be selected.
The command must be used each time a selection is made.
See Also
Select - Click Joint in XY Plane
Select - Click Joint In XZ Plane