Copy and paste the "747-8i.ini" and "747-8i.jpg" files into your FSPassengers/payload_model directory.
INSTALL THE SEATBELT SWITCH INTO THE VIRTUAL COCKPIT
Copy and paste the following text:
"gauge21=FsPassengers2004!cabinsign, 667,9,38,35"
into the "...b747-8i/panel/panel.cfg" file, underneath the [VCockpit01] section. This is located at the bottom of the file, so you'll have to scroll down a bit. Be sure to place it on its own line, below the "gauge20=..." line.
Next, if you haven't done so already, copy the "FsPassengers2004.gau" file into you "Gauges" folder.