[4.7.5] Cannot assign other components to blueprint script variables

I got a behaviour script which simply outlines the mesh which the player currently looks at (“isSelectable”). It has to work with actors as well as with actor components inside of blueprints.

But when I try to assign other components of the blueprint as variables (here: static mesh components) I simply can’t select anything:

(Background: This script should highlight all the other assigned meshes as well, the other wheels for example).

How do I get a reference to other blueprint actor components from my blueprint script?

Many thanks!