I came back from vacation (20 days) and my 2006 XC90 wouldn't start. The key fob wouldn't unlock which was the first indication and then I just had absolutely no lights so I assumed it was a full drain. I tried jump starting it to no avail so I took the battery in and they confirmed it was drained and the diagnostic report suggested a new battery. I ended up putting the new battery in and after running it for a bit noticed that the fog lights stayed on after I had turned the car off. I tried turning them on and off manually but they would still constantly stay on.
I've disconnected the battery for now to not have it drain again but I'm at a loss. I don't know if this is what caused the original battery to drain or if I shorted something while jumpstarting / removing / installing the new battery (absentmindedly connected the + first instead of the - when installing the new one and had the car alarm go off).
I've checked the fuse and everything seems to be in order, I might check the relay but it seems to just be the fog lights that are staying on and not related components, plus I doubt a relay would weld itself connected, it would make more sense if the lights wouldn't turn on.