You can’t add XRay but you can edit the Edge colour (to a grey colour) and the materials to a 50% opacity (or whatever you want and Then bring the component back into your original model.
It’s arguable whether this is quicker than other methods, but it does work and is a valid approach.
Adjusting materials to 50% will create a copy of that material when you brin it back into SketchUp but ti’s not too difficult to delete and repalce it back to the original “solid” material.
I just realised also that Steve Mouzon created this original post… awesome to have a renowned architect & urban designer on the forum, and from a studio that creates some brilliant 3d images. 
Thanks so much @AK_SAM! Just trying to figure stuff out. Fortunately, SketchUp makes it easier than most.
…is also a familiar star from the PowerCADD user world, which is why I understand the request so well. (
Steve) I was hoping he’d show some examples of drawings using this feature, but you can at least see examples of his stuff in the PowerCADD “Drawing Room” here:
Sorry, did I say X-ray? Don’t recall. Anywho I agree with reducing opacity ( make more translucent ) ( or is it transparent?). What’s the diff? at least you can see through it betterer, ya know?
Essentially, you edit a material, color or image to reduce the opacity in the Materials (edit) section of SU.
Another vote here for this feature.
Would be very useful for showing internal engineered structures while also keeping ‘simple’ objects like walls and roof visible.
A note though, ticking a box to ‘x-ray’ a tag to which a parent component/group is assigned must override the material settings of all other tags assigned to sub components/groups buried within the parent object.
Not sure the above is clear but hopefully it makes sense.