I have had problems with my auto on/off for a few months. At first, when switching to Auto, the lights would come on at night, but would go off when I switched to full beam. Now the lights will not come on at all in the auto position. THey work fine in manual position. I am guessing the sensor is the issue? Does the same sensor also control auto wipers, as this seems sporadic too? Any suggestions appreciated.
Thanks!

 

Most common cause is a broken/disconnected wire in the multifunction switch.
I had the same fault with a recently purchased XK8.

I pulled the switch from the column and soldered the wire back on the appropriate terminal.
Should be a YU (Yellow/Blue) wire.

 

The auto-headlights sensor is in the rear view mirror (at least is on mine) with the rain sensor being the separate sensor on the windshield. My auto headlights stopped working after I switched to an Acura TL rear view mirror without the sensor, but as my old mirror had a broken ball joint and couldnt stay up anymore, this was a tradeoff I was willing to make.

All that to say, start with the easy stuff, clean all the sensors on the back of the rear view mirror with a q-tip.