I have a 2000 Expedition (5.4).
The left license plate light is not working. I tried several new bulbs and even changed the electrical socket, nothing made a difference.
The right side works fine.

Any ideas what could be the cause?

All information appreciated.

Thanks.

 

broken wire, although it most likely would have casued a short and blown the fuse makeing it very appearant.
check anyway, right behind the bumper, i would follow the wire until it reaches the weather tube. (most likely not broken in there)

 

Check the ground, the contact between the light socket and the bumper is usually the ground, if it's all full of dirt/rust clean it out, lightly sand and put some grease on it.