the connectors on the back of my headlights do that sometimes, they'll just stop working. I need to wiggle the connector and push it back up tight onto the bulb and they're fine. Unplug and re-plug in all your connections at each light. You may find one or two to be corroded a bit. They can be replaced or cleaned, depends how bad they are. I use a small piece of sandpaper folded to slide in and out of each connection, then sand the leads and reseat everything.