When must attachments have additional lighting systems?

You answered correctly. According to German traffic rules, attachments on a vehicle must have their own additional lighting systems if they affect the visibility or signaling of the vehicle. Specifically, if the attachment blocks the vehicle's existing lights, extends more than 40 cm beyond the vehicle’s front or rear position lamps, or sticks out more than 1 meter beyond the vehicle’s reflective devices, then separate lights are required. This ensures that other road users can see the full length and width of the vehicle plus its attachments, maintaining safety during driving, especially in low light or at night.