[DanEC]

I took one of the bulbs last night and tested it with my battery charger. They work fine - they are dual intensity and light up from either contact, one being much brighter than the other. I know my taillights and wiring are good so it apparently has to be some sort of issue between the socket and the bulb. I'm going to remove a tail light so I can examine the socket better and see if I can figure out what the incompatibiity is.