Master Caution Gauge in undocked window

Hi folks,

I am building home cockpit and using a 23" monitor for PFD and ND displays (in zoomed undocked way). I want to, similarly, create a new window (and undock it) with just the master caution gauge - the yellow button and mini display which is right next to it. I've tried various ways with creating new [WindowXX] section and gauge00 pointing to pmdg737_Main!MasterCaution gauge - to no avail... The window gets created and I can even undock it, but it is black inside.

Can someone suggest what needs to be done? Thx!