If its failed it could be the switch itself, the motors in the headlights or mechanical connection between the motor and the headlight unit.
With the engine off but lights on, parked against a wall, ideally at night, under the light of a full moon, while Venus is near Uranus (haha) ....open the drivers side window, lift the bonnet and get out. stood next to the car reaching in so you can get your ears as close as possible to the headlights, move the switch.
- If you see no movement on the wall and hear nothing the motors are not being told to move, so its likely the switch or circuit
- If you hear noise and see no movement the headlights assembly inside the unit has come away from the splines on the motor
To fix #2 above, using the headlight adjusters on the back of the headlight (bolts) wind it all the way down so its pointing at the floor, then try the switch again. This should have put the inner light assembly back as close as possible to the motor to allow it to bite. If that worked, carefully adjust the light back to optimum viewing angle while checking the electronic motors have not come away from the spines again.
I found, during several headlight modification sessions due to project Halo work, that the motors can be literally separated from the headlight assembly by over adjustment! Its like a ball and cup on the end of a winding rod. Adjusting them all the way back pushes the ball back into the cup.
If its the switch itself, easiest first fix is to get electrical contact cleaner and spray tons of the stuff into the switch while operating it (vigorously) for a few minutes just to make sure its not a carbon build up on the contacts from lack of use.