Airspeed variable in FSDS2

I want to use airspeed as a display variable in FSDS2. I have searched this forum (and others) and have seen it talked about a great deal, but have not seen a definitive answer. Can someone shed some light on this please. I have even used 1 to 16384 and the part remains invisible. Also,How can I add a pre-process display condition in FSDS2? I want to add cabin lights to the variable display preset list. I see an xml file FsConstants.xml giving, for example, 0x0100. Is it a question of adding 0xxxx with the correct xxx number? Many thanks,Nick.