Driver's side reverse light not working

[PbFut]

Remember, it's a one wire socket so you need ground. I would attach one lead of meter to good ground, then check the +12v pin in socket. If the socket and or housing is free from truck no risk of shorting. If housing still attached to truck careful with your probe. To verify housing is properly grounded, check ohms from socket lip to a good ground point. You should not see more than 1 to 3 ohms depending on how clean the contact surfaces are and distance between each point. Since the other side works the problem is going to be close and easy to find.