I'm not sure where it is. I have the same problem. Mine havn't worked in about a year. But I looked and since none of the fuses were blown, I didn't think it was the problem. I may have overlooked something though.
2002 Dakota sport 4.7 5 speed, 4x4, 159k
Fuse #26 in the fuse panel on the drivers side of the dash.
Thanks. That fuse is fine (checked visually and with a meter), so I guess it is most likely that the backup light switch is bad (since both lamps are not working). Is it much of a job to replace one of those?
The problem was the reverse light switch. These cost about $15 from an auto parts store (significantly cheaper from e.g., RockAuto.com), and installing a new one brought both reverse lights back to life. It seemed like an easy job (especially if the vehicle is on a lift), because it only took my mechanic about a minute to do it.