my connectors do this, one light would frequently wink at oncoming drivers.
It was the connections right at the headlight. With the lights on, wiggle 'em. Push/pull, anything to see if they turn on. You can also pull the connector off and see if there is any coorosion inside the terminal end. Sand the connectors inside with a folded piece of emory paper then sand the connector on the headlight and put it back together. I also had to bend the tab on my new lights upward in order for it to make a good connection.
Im considering just putting in new connectors or soldering the wires right to the headlight terminals.