If the headlight switch recall has been done, check the switch to see if the ground wire fell off. Mine had to be bent to allow the connector to clear the def duct and the tech must have done it with the connector in place because the connector (female spade) was just sitting there, not tight. I used a pliers to finish bending the male spade (it is part of the updated switch assembly) and then squeeze the connectore back down so it would grip tight.
I think you have to remove the switch to see this and it isn't there unless the recall has been done.