Reply to "Adding red taillight to P.E. observation car?"

I bought an eBay kit to do this on my O gauge observation car.  The original jewel lens is easily popped out with the tip of an Exacto knife blade tip. If I recall correctly, the hole is 1/16". The trick is to slightly angle the hole down so you don't punch a hole through the top of the car. I painted the inside of the hole flat black to ensure the light doesn't show through.