I'm having similar weird headlight issues. 2006 4.8is with xenon headlights. The driver's side doesn't come on most of the time. If I mess with the switch, going from off to auto I can usually get the driver's side to come on and then it will usually stay on until the next key-off and when I start it again the left is off again. Back to messing with the switch, it will also occasionally cause both headlights to be off when in the auto position, and on rare occasion, even the passenger side will be off while the driver's side comes on. I feel like it's either in the switch or in the Adaptive Headlight Control Module but hate to just throw parts at the problem. Only 30,000 mostly dry Southern California miles on it. No snow or salt but we have had a lot of rain. I guess I'll pull the glovebox door and see if the module is wet or anything else in there is. Almost always garaged and all windshield trim seems excellent. I did just replace the alternator as the old one was pushing over voltage which played havoc on a lot of stuff. Driveability problems mostly as the engine electrics were not happy at 18 volts. I think that might have cooked the headlight module, or something . . .