Assuming they worked fine the last time you had the trailer connected, have you tried to unplug and replug your trailer connection? Sometimes the connector isn;'t making a good contact. Corrosion is the enemy of us all.
If that's not the case, take off the cover of the trailer pigtail and see if one of the wires has come loose. with the cover still off, plug in the lights and wiggle the wires on the pigtail connector to see if you get contact.
These of course are the quick and easy fixes.
Mark, Vicki, & Scout THE dog
2015 Hemisphere 282RK
2010 F250 Super Duty
1992 Goldwing Aspencade