I believe the 850 and S/V70 work the same. The floor light only comes on with the selected door. The red lights in the door jam will also illuminate along with the rear door red lights in the rear, both sides, but not the opposite front door.

Check that switch and the bulbs. If the floor bulb doesn't come on and the red lights do, probably a bad bulb. If the red lights also don't come on, try pulling the switch toward the driver's seat.
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Keeping it running is better than buying new