When testing you light configuration within the simulation, the light source looks something like this:
The light source is located somewhere behind the dashboard.
You have to set the attribute "Inside the vehicle?", so the order of the light source is right.
This setting is important when you define the light source for a turning signal. In this case the light source should not emit into the vehicle by deselecting this option.
The pictures are taken from the R2.2b (R2D2) built by Team ViewApp.