These rear light clusters have long been a feature of continental trucks, both rigids & semi trailers. They have been most popular in France & Germany.
Dependent on the country & trailer manufacturer, the lights are wired differently. Sometimes both ‘red’ chambers are used as both side & brake lights, and sometimes either the top or bottom chamber is used for side lights, and the other chamber is used for the brake lights. Either way, they are very typically continental, and very effective.
In the model form these lights can be wired to represent either style, but they are fiddly as there is no light board available.
In the kit you have included: 2 housings from aluminum with 3 chambers (which can be lighted), 2 red and 2 yellow glasses, diameter ca. 11mm, height ca.6mm.