5v should work fine, so I'm guessing you're doing something wrong? Or it could be your socket? I also notice that in the pic, the wires are just wrapped around the lugs, rather than soldered. Theoretically that could work, but it could also be the problem if there isn't a good enough connection.

If you have a DMM, test the voltage at the lugs of the socket you're using.

Try the bulbs in a pinball machine first. There could be a bad bulb from us once in a while, but having multiple bulbs all not work is basically unheard of.

Also, once in a while, you'll come across a bayonet bulb with a thin clear film on the bottom that is preventing a connection. Just scrape it with a fingernail and try again.

And thanks for the kind words about Purple Passion! OLDPINGUY deserves all the credit!

Actually, when testing the voltage going to the socket, do it without a bulb, and you'd want to measure with one lead on the main barrel of the socket (where the edges of the bulb rest), and the other where the point of the bulb comes in contact (on the inside bottom, or on the nub on the outside bottom).