How do you mark a load when it extends laterally by more than 0.4 m beyond the side lights of the vehicle?

Your answer is correct. When a load extends more than 0.4 meters beyond the side lights of the vehicle, German traffic rules require that it be marked with white side lights to the front and red side lights to the rear. This ensures that other road users can clearly see the extended load at night or in poor visibility conditions, improving safety. Simply using reflectors or assuming no marking is needed up to 1 meter is not sufficient according to the rules. Remember, the key point is to use lights with the correct color in the correct positions to indicate the extension of the load clearly.