You have to change a tyre on the hard shoulder of the motorway. What safeguard is necessary?

Your selection of all three safeguards is correct and adheres to German traffic regulations for ensuring safety when changing a tire on the hard shoulder of the motorway.

1. Setting up a warning triangle at a distance of 100 meters alerts other road users to your presence and the hazard of your stationary vehicle, reducing the risk of accidents.
2. A warning light further enhances visibility, especially in low light or adverse weather conditions, providing an additional indicator of your situation.
3. Wearing a high-visibility vest ensures that you are easily seen by oncoming traffic, which is crucial for your safety while attending to the vehicle.

Together, these measures are designed to protect both yourself and other road users in a potentially dangerous situation. Adhering to these guidelines is mandated by German traffic law to promote safety on the roads.