Running lights but no tail lights on trailer

[Shorelunch]

I have a flat 5 pin connection and LED tail lights. No brake lights, turn signals or tail lights when headlights on - on either side, but the running lights work. I checked fuses on the tow vehicle and they look ok.

Where do I start looking now?

[Jeremy airjer W]

I'm guessing that the brake and turn signals work with the headlights off?

If that's the case you have a ground issue.

To check the vehicle use a test light connected to the mail terminal of the vehicle connector. Turn on the lights and probe the female terminals. the test light should illuminate on the terminal with the brown wire. If it doesn't than the vehicle ground is bad.

Check to make sure the white wire has a good connection at the trailer. Depending on the construction of the trailer it may be necessary to run the ground wire all the way to the light assemblies.

[Shorelunch]

Actually, there was no tail lights no matter what. Hooked up another vehicle and same issue.

Dealer looked at it right away this am and I guess there's a second harness for just the rear lights that they replaced and everything's ok now.