huawei e800 expresscard modem not being recognized by manjaro

I'm trying to get a expresscard / PCMCIA card modem to work in manjaro linux, but modemmanager is not detecting it at all, let alone let me configure a connection with it. The status light is blinking blue every 2 sec. or so. I know (because it worked on the same laptop under ubuntu) that it shows permanent green, if it's ready for use. Any pointers where to start, what to check, etc.? I also used modemmanager, but that doesn't detect anything either.