Driver side rear signal light is out
Did you see if the fuse has blown? if it's ok did you try to replace the blub?
Which bulb is out? All three or just one? Is the lens cracked? Does water get into the lens? Corrosion inside the sockets causes a lot of these problems. Remove the bulb and see if the contact points of the bulb or the socket shows signs of rust. Check with a multi meter. Fortunately, if that is the problem, replacement sockets can be purchased at most auto parts stores. You'll have to splice the wires together.
Search Ford Explorer Questions
Ford Explorer Experts