If you have a 7 pin connector and a battery in the trailer you can use this diagram to test things out.
If you have a test light or volt meter test for voltage between 1 and 7 o clock. If you have voltage your trailer battery system is good. If that is the case now using the front view of the connector place a short section of #12 wire in the battery slot, at 1 o clock, and then touch the other end of the wire to the parking lights and see if they come on. Do the same with the left and right signal lights, 3 and 9 o clock. If the lights work with this test your problem in in the TV wiring.
If you have voltage from the battery and these tests do not produce lights in each test you have a wiring or ground problem in the trailer itself. Check the grounds at each fixture first as that is the common point of failure.
If the grounds are good you will have place the test wire in a circuit and test for voltage working your way back to the fixture at points of connection. First point would be just inside the trailer where the umbilical cord is connected to the trailer wiring and then at the fixture itself.