I haven't find anything about this. I owns a 1996 Volvo 850 GLT wagon. The light switch is off and the exterior (signal, headlight, tail) lights doesn't turn off during daylight whenever I drive like it wasn't in dark at all. I knew it's not right. It may be the switch or solar sensor - I think I'm wrong. Any clue?

 

My 850's don't have any sensors. When they're off, they're off. when they're on, they will turn off when I shut the engine off, so I leave them on an awful lot.

If yours can never be off, then either the switch or the headlight relay is bad. I normally would not suspect the headlight relay on other cars, but on an 850 it's a big complicated "solid state" thing. Might have some brains in it that went bad.

 

Just a side note if the lights are on in the parking light position they will stay on after the engine is off, in the full on position they shut off with the engine

 

I recently found out from the owner manual book:
https://imageshack.com/i/kpsFNWTMj

It's funny because I didn't know we can adjust the screw (in bottom right of the light switch) to either position. I changed it to "All lights off" (\) and it works perfect. Good thing, I didn't mess with the relay and others. I don't like running daylights much and I'm keeping the light bulbs life last longer.

 

Daytime Driving Lights Settings on Volvo Cars - A…: