Tail light stays on

Find out what circuit powers it. Pull the fuses one at a time. Maybe it's a bad light switch. Unplug the switch. Examine the diagram to see what in the car is "hot" at all times Brake circuit, trunk light, dome light, cigarette lighter etc. There are not that many fuses. It would not be long I'd have the cluster out and or the seats out to examine under the dash. Look for suspicious parts of the harness