Hi Lukas,
not sure, if this is still open…fought for the past two weeks with similar problems - and for my opinion also the Wiki is wrong: The group address is “A, B, C, D…” for the classic series - and not “I,II,III,IV,…”
ALSO, it’s not possible to use the absolute device name in the openhab.cfg:
This one works:
culintertechno:device=serial:/dev/ttyUSB0
And this one doesn’t work:
culintertechno:device=serial:/dev/serial/by-id/usb-FTDI_FT232R_USB_UART_A700RHJK-if00-port0
If someone else looks for a solution with Intertechno problems, here is it how I got everything working:
openhab.cfg:
####################### Intertechno (Licht) #######################
culintertechno:device=serial:/dev/ttyUSB0
culintertechno:baudrate=38400
culintertechno:parity=none
culintertechno:data=8
That’s the item definition:
Switch CUL_Licht_TV_Halogen { culintertechno="type=classic;group=A;address=1" }
And this is what the sitemap looks like:
Switch item=CUL_Licht_TV_Halogen label="Licht TV (Halogen)" mappings=[ON="ON",OFF="OFF"]
Let’s hope, it saves some other people those needless hours I had to spend. But now it’s working 
Cheers,
Boby
P.S.: Using now an original CUL from busware - and here’s the address of the stick /dev/ttyACM0