Hello, new to the site.
I have two(!) '99 Bonnevilles, both same burgundy color. (yes it is confusing sometimes) The only difference other than mileage is my son'* has a trailer hitch.

On mine, the auto headlights recently ceased to come on automaticly.
All else seems to be right. I miss the convenience. Where to start? I have already done the put your finger over the dash button thing with no results.

Thanks in advance,
Bob

Try to do a search on the site about this, I know I've had this issue on my old '95 SSEi, and the headlamp switch with the Twilight Sentinel had pretty much melted, and I had to buy a new updated head lamp switch and fix the wiring.

You can pull that light sensor out. When you do, the lights should come on. If this happens, the light sensor is bad.

95 was the last year of the melting connector (only year really). I'd go after the light sensor like Cheetah says. Then if that makes no difference, inspect the headlamp switch connector.

(I know your confusion.....look at my sig. One has a hitch also)