Just bought a 2006 with 92k miles for my son. One reverse light is out. We changed the bulb but that didn't fix it. What's the next thing to check?

 

check to see if there's power going to the socket. if not, you'll have to trace the wires to find the break. if there's power to the socket, either you got a bad bulb or the socket is damaged. replacing the socket would then fix that issue.

 

Had an issue myself last summer with my 2008.

As I recall, there is a wiring connector just before the taillight itself. You can see it if you pull off the tail light. The connector corroded. Only had some lights on that side of the tail.

Couldn't find the replacement connector itself. Landed buying an aftermarket trailer harness for the Dakota and utilized the connector off of that.

Took some pics at the time ....