RE: Graupner Mosquito
After the tail is assembled, including control horns, it is glued onto the fuselage. I made some control horns from thin plastic and CA'ed them onto the elevons.
The control wire is cut to length and then bent 90 degrees to fit through the hole. I felt that nothing is needed to keep the wire in place on the control horn due to the natural spring tension.
It's important to make both sides symmetrical for optimal flight control.