update: replaced my bcm. now the drb3 emulator can communicate with with the bcm and clp.
i deleted all stored DTC from the BCM and after that i did the "system test - retract spoiler 1sec" and the spoiler went
down a little each time i did. after 4 times or so the spoiler was fully retracted! the spoiler up/down button is still dead.

i will find out how to measure if the switch is simply not connected to the bcm and will update again.

edit: i found out the drb3 emulator can test the led of the spoiler up/down button. the led lights up.