NSS / backup lights question

essentially that's what i did... i crossed the white and the purple wire, which should've brought the lights on. but it didn't work.

question: the bulbs only have a single wire going in, but do they work by grounding the sides of the bulb to the car body? i put some silicone anti seize on the socket so i wouldn't have any problems taking them out but now that i think of it, i wonder if that's preventing the current from grounding.