For the trip to the Texel ferry you have bought two bright extra LED lamps. You want to screw them onto the back of the trailer, because more light seems safer to you.
Simply fit them, as long as they are clearly visible
Fit them, as long as they light up together with the car lights
First check whether these extra lamps are allowed at all
Explanation
False — You think lighting up with the car makes extra lamps allowed. Working together with the car is a requirement for the compulsory lights, not a permit for extra lamps: extra lighting is forbidden in many cases. Book p.232.