trailer tail lights not working. What is the next move

If none of the lights are working check the ground wire to be sure of the connection. Also check the connection plug to be sure of a good connection. Can check the connections on the lights.

I had the same problem. At first, the lights were very dim, then stopped working completely. Replacing the bulbs did not help, so I replaced both complete light assemblies. That gave me taillights but no brake lights or turn signals. I suspect the problem is in the harness, so I'm going to replace it. I strongly suggest you make sure the replacement light assemblies have pigtail connections that you connect to the harness via wire nuts or in-line crimp connectors. The original lights are wired with push-in type connections. This gives very poor conductivity and if one comes out, like mine did, it is ridiculously difficult to re-install it.

If the lights were working before, take the bulb to an auto parts store and get another. If the lights did not work when you got the trailer, check the connector to your truck. It's most likely the ground wire not making a connection.