PaulNJIT

I have a 2010 ford fusion. About a week ago I realized that both my headlights were dead. I bought and replaced both headlight bulbs. A day later I noticed that the passenger headlight was out, but after disconnecting and reconnecting the bulb it worked fine. A few days later the same thing happened on the driver side. Last night I got home, and both lights were out again. Why would both lights be working sometimes and not other times?