Why do the interior lights stay on when mydoors are shut in my 91 Toyota 4Runner?

The interior lights will remain on for a duration of time after the doors are shut as a safety/courtesy feature. The reason they remain on is the capacitor in the lighting electrical circuitry. The capacitor passes on energy when the circuit is powered, and retains voltage when the circuit is powered down. Once the circuit is powered down, i.e. the vehicle shut off and doors closed, the capacitor still holds that charged voltage and discharges itself over a period of time, usually 30 seconds or so. As it discharges, the electricity moves through the circuit and through the bulbs until the capacitor is completely discharged. Hope this helps!