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the housing itself is plastic. the lens part of it will pop right off the back, just squeeze the sides a little. the housing is held in place by a couple of rivets, so you'd have to drill them out to remove it. you can either rivet it back in place or use drywall anchors and screws. the bulb inside is a festoon style bulb 40-42mm long, the type that has the hoops on either end. I replaced mine with an LED bulb but there aren't any that I'm aware of that are a direct drop in replacement for the C5 due to the direction of the clips.
the light turns on and off by a gravity switch. if you need to disconnect it for a car show the connector is on the radiator shroud directly under the light housing.
I don't know what the part numbers are but if you are in need of a replacement (or extra) contact Gene Cully at www.gmpartshouse.com and he'll be able to tell you everything.
4GTABODT is right about the PN for the bulb,but make sure you are quick with your fingers when you install...the bulb gets freakin' hot in a hurry ......or you could disconnect first, probably smarter !!