When testing you light configuration within the simulation, the light source looks something like this:
The light source is located somewhere behind the dashboard.
Solution:
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.