When i shut the car off the brake lights remain on.

If all three brake lamps stay lit, including the center, it's probably the brake lamp relay which is located in left rear side of vehicle in the fuse block compartment (that hidden one covered with carpet). Volvo usually uses ID "RMI5" - that's as close as I can get you. If possible, try testing first by using an existing "good" relay back there. Any should work if the spades match up. Check around for moisture - should be bone dry, but I've heard of techs drilling holes up from the bottom of the vehicle into that compartment to run accessory wiring and not sealing the holes they've created.

There's a switch on the brake pedal arm that turns the light on when you press the brake pedal.
The switch needs to be adjusted or replaced.
Hope this helps.

This is most likely a short in the instrument panel's(IP) logic chip. As long as you can start the car everyday, you can live with it or have the IP diagnosed and replace it. If you ever plan to leave it for a week or two. Disable the radio and nav systems if you have to, then remove the negative side of the battery. This light will drain the battery over time.