Working with translucent parts is... not easy.
Don't I know it.
Here's a tip. If you're using Blender, anyway. If you're not, there should be some equivalent to it.
I parented all the parts that are made of self-illuminating materials to an empty. I don't think this was necessary, it was just for organization.
However, what I've found is extremely helpful for things not looking stupid (such as your mirror behind your window not being affected in color by the window in front of it
) and various parts of the car disappearing / not casting shadows is creating an empty, naming it whatever (I chose zflarecontainer because it was mostly for the flares on the police car, with a z to put it at the bottom of the list), and parenting all objects with translucent materials to that empty shape. (Every object in there is JUST the translucent part of each object. I also made sure that the translucent materials were removed from the material lists of every solid object)
Somehow this helps the .dts format or Blockland or something along the line to recognize that, hey, the translucent stuff REALLY IS a separate thing from what it's around. If you leave them unparented and floating around with the other stuff, even if the translucent-material objects are separate objects, things like this tend to happen:
