I have an old lamp post outside my house with five globes. Recently two of them stopped working. I don't know much about electricity, but I've checked the wires at the bottom of the post and everything is connected and working there. At the top in the socket, I'm not getting anything. I tried sanding out corrosion, but I'm not sure what else to try. I can see the connections of the light socket to the rest of the wiring and they seem to be connected. Is there anything obvious that I'm missing before I call someone?