Old Faller relais 649 can be used as a simple switch, e.g. to turn on the lights when the train passes desired location on the layout.
I am helpless how to connect it. Light bulbs can be connected in two pairs (green pair and red pair - plugs 1, 2,3 and 4). There is a pin inside, which moves through the solenoid when activated and closes the circuit, either I or II. But that`s all I can figure out.
Where is transformer connected and how ? How to connect Kontaktgleis ? The solution should be in three plugs on the opposite side (blue - yellow- blue).
There is a schematic drawing in 649 manual, but it is not well explained, still - might help someone who is more familiar with it.
Thanks for your kind attention and answers.

If so, transformer must have two connections L and 0 (Masse). Where is Masse connected ?

Thanks Fabrice,
I tried in several Maerklin groups. You are the first one with clear explanation. No wonder France is the only nuclear power in Europe. We all rely on you and your technology and determination. Best regards.