^ what Les posted is correct
I would suggest checking the leads like he said, with the bulb plugged into the socket
then if you have 12 volts on the low and high beam terminals, using the ground terminal on the back side of the lamp socket, and the lamp is not on
then either the terminals on the bulb or connector are tarnished and not connecting, or the lamp has failed.
Plugging the volt meter into the lamp connector by itself is usually a good test 99% of the time, unless there is a high resistance connection back in the wire harness somewhere. With no lamp connected a high resistance somewhere between you and the battery will still show 12V on the meter, but when you plug the lamp in no current can flow, and you will be singing WTH?! WTH?!