1998 Ford Explorer Autolamp feature malfunctioning

Electrical problem
1998 Ford Explorer 6 cyl Two Wheel Drive Automatic 75, ooo miles

Weve never used the automatic headlight feature at all, and have always only used the manual dashboard headlight switch. The "autolamp" slider switch, which is built-in on the interior rear view mirror is set to the "off" position, but no matter what we try, it has a mind of its own, and now our headlights won't shut off until about 3-minutes after the engine is turned off. How can I deactivate/override the sensor for the autolamp, and where can the sensor be found? On the mirror itself? Somewhere in the dash area? Is there a fuse I can pull? Where? Please help. We want to be able to turn off the headlights manually. Thanks!