Contact the vendor you got the light from, you're missing the "Tail Light" socket (defective part). Get them to confirm it should have two single filament sockets just like the left side.
Also, the Passenger car housings are not the same as truck, the truck BOW TIE lens is 5" tall the car CHEVROLET lens (for the cars that used that style light) is 4-5/8" tall.
The lens should have the convex circular area to the top with the Stop Light shining through it and the reflex markings at the bottom for the Tail Light/Tag Light.
Mike B
