It COULD be the 7-pin connector, but the current to the tail lights comes all the way from your tow vehicle battery, so the problem could be anywhere along that path to the tail lights themselves, including inside the trailer.
When you say the tail lights are not working, do you mean the brake and turn signal lights, or the night time running lights, or both? And, are the other running lights on the trailer at the top front and rear working?
You can buy a simple 7-pin plug tester that you plug into the 7-pin socket in the tow vehicle to check ALL the outputs at that point. I highly recommend you get one of these. This is one like I have:
https://www.amazon.com/CURT-58270-Ve.../dp/B001EOWQY4
If all those circuits check good, the problem is on your trailer side. You can check all the running lights in the trailer, their circuits, and the trailer plug part for them with a simple turn signal flasher, as discussed in Post #2 of this thread:
https://www.hilotrailerforum.com/f11...-ft-hilo-5381/
If you make a couple jumper wires for the flasher, you can connect the trailer's battery to each of the brake/turn signal lights for the trailer too. You simply have to connect the battery +12V blade to the appropriate brake/turn signal blade. This would be the 11 o'clock to the 9 o'clock (right turn) and then to the 3 o'clock (left turn) positions, I believe.
I think the most common cause of non-functioning lights is rodent damage to the wires inside the trailer. I had this and had to replace one wire. Then, I "rodent-proofed" the trailer!
- Jack
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