What light bulb is this?

That's not a 12v bulb, but I do know what it is, cause I have bought them this year for the kid lamps.

http://www.amazon.com/Lava-Lite-5015-6-Replacement-10-Inch/dp/B004CLYOJ6/ref=sr_1_1?ie=UTF8&qid=1417904508&sr=8-1&keywords=kt120v15w

Looks like a candelabra base. Are you sure it is 12 volts DC?
Look closely around the base right where attaches to the glass for markings.
Look closely around glass right at base for markings in the glass.
Test socket for voltage.