The glove box light remaining on leading to a dead battery in a few days is very common in older 850s. Unfortunately, it's kind of like a refrigerator bulb in that you cannot always tell if it's gone out when the glovebox door is closed.

All mine needed to fix it was to get the switch to depress more than the glovebox door was pushing it. I put a felt tab (the self adhesive type that you would put on a chair leg to keep it from scratching the floor) on the inside of the door where it aligns with the switch. Problem solved.

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"Differences of opinions should be tolerated, but not if they're too different" - Sharon Craig