Here is a dome light assy. removed from a 42 Dodge car.  Light is nice, very nice chrome, and glass lens.  Has the bulb holder assy.  6 volt bulb untested.  Wire lead cut but has a screw on the light lead so you can put a new wire in this.  back part was held in place on the roof with 4 screws.  Light might be the same as other Mopar cars from the early 40's but you need to research this to see if this is right for your car.  Would make a nice part for a Rod.