Fossy

Up your shaders, see if that works.
 
Note: On downloaded cars that don't use siren coronas, there won't be any environmental reflections or vanilla=style "flashing". An easy way to tell if your car uses coronas or not would be to flip the car with the lightbar on and look under it - if there are lights under your undercarriage, the car doesn't use coronas. A lot of modders put their coronas well down there so they can have all-blue, yellow, or other light colours in the lightbar without reflections being off.