None of the default FSX planes have actual logo lights. The 737 tail logo is displayed when the environment becomes "night" and the b737_800_1_LM.dds file is displayed. This file also makes the cabin windows apprear illuminated.
I modified my b737_800_1_LM.dds to make the vestibule appear lighted when the door is open as well as properly "illuminate" the logo by performing a Multiply in my graphics editor for each carrier. That is, I don't have just one LM file but a unique one for each airline.
The logo switch in the 737 issues a command to turn on a type "9" light. Since there is no true logo light for this model, I use that switch to turn on the nav lights as seen below in my aircraft.cfg file modification:
light.0 = 9, -24.20, -56.60, 3.90, fx_navredm ,
light.1 = 9, -24.20, 56.60, 3.90, fx_navgrem ,
...
light.8 = 9, -29.50, -56.60, 3.70, fx_navwhih ,
light.9 = 9, -29.50, 56.60, 3.70, fx_navwhih ,
I went so far as to edit the graphics of the overhead panel to say NAV instead of LOGO.
Peter
Here is the LM file before and after my edit, and the result with open doors and lighted vestibule:
This is the original file.
Note the airline-specific tail logo and the new graphics in the lower right. This is how you "illuminate" the interior.
Note the open doors and the newly illuminated vestibule.