I' have a 1999 JGC that I've owned since 2000 and in those 19 years I've never turned the headlights on or off. I've always left the switch set on "auto". Today I got in the Jeep, during daylight hours and the headlights
were on.
At the end of a short trip they were they were still on. Turning the switch to the off position the lights will go off. Turn it back to "auto" in daylight and the lights came on.
I know it's not really a big deal but so far I've managed to keep everything working as it should and I'd like to continue that. I haven't checked anything yet but it seems to be that it's not sensing that it's daylight and the lights shouldn't
be on and as to where that sensor is I have no idea. I have a Haynes book but on this it ws no help. Or could it just be a relay under the hood?...or the ecu?

 

Do you know where the ambient/photo light sensor is located? It should be in either one of two or three locations. Probably it is a small dome looking bubble with a tinted lense located on the top dash centered near to the defroster vents. It is either located there, or it is in the backside of the center rearview mirror. If it is not in either of those places.. it is sometimes actually located underneath of and inside the top of the dash inside of and/or near to the defroster vents.

The ambient light photo sensor is probably either covered up by something (a hat, paper, or anything), covered in dust, dirt, or cigar/cigarette smoke film, or else it has failed and is probably in need of being replaced.

 

I found it from some info on an unrelated post on another forum. He mentioned that on Jeeps with factory alarms (red led in a small pod on dash) the headlight sensor is located on the front side of the pod. The sensor is a little clear lens about 1/8 inch in diameter. And, for once in my life I had put a padded envelope on the dash covering the sensor. The sensor figured it was always dark so the headlights were always on. Took the envelope off the dash and everything works. Cheapest "repair" ever.

 

That was my guess for what it most likely was too.

Those photo sensors do not ussually get too much dirty film on them to cause a problem like this, or to just go bad like that either (although of course they can).