What is the correct size bulb for a 1966 transmition light (courtesy light that lights up P R N D 1) and Where do you push the bulb through-those prongs-cant find where the light is supose to mount Thanks Scott

 

When I test the socket (positive) side with the tester it lights up-every time I put a light bulb in it doesnt light up and the bulb burns out-I have been trying 12v "57"
I must be missing a piece because I cant find any hole to push and mount the bulb in....
any help??