Trailer Brake and Turn Issue

No. I check my TT lights frequently, such as two days before departure, without hitching up.

You shouldn't. But, if you have a problem with the wired ground sometimes it will work thru the hitch so you don't notice the problem. Any time you have multiple things not working, or most of the time really, trailer wiring problems come down to a bad ground wire.

What is your tow vehicle?
Many newer rigs have fuses for the trailer light function. Check owner's manual or the fuse panel under the hood. Note, note all vehicles have them and location may vary.
Why did you have to replace the wire harness?

It was busted, got rear ended some time ago and Hitch took the brunt but snapped the plastic housing for the 7-way just enough it would just teeter when you hooked up the plug.

You could have had brakes on and it shorted or went to ground and blew a fuse.
Make and model of tow vehicle?

2013 Nissan Frontier

I looked up your owner's manual. It does not list fuses. It refers you to the fuse block cover.

Yep... You will have to pull the cover. Probably the one under the hood. It should have a diagram map on the inside of the cover and show the "trailer" fuses. there should be stop, right and left turn signals to the trailer plug I would think..

Just tossing that out there, as I don't understand why the manual does not list the fuse diagram?? My Ford F150 does.. :)

Good luck! Mitch

Yes I looked at the standard fuse box, it's next to the glove box, and there's not Trailer brakes listed on the legend inside the cover. I'll look under the hood for the other fuse box and see, but that seems odd to me that It would be there. We'll see.

THIS is for a 2016 trailer running light fuse but will give you an idea of where to look.

I think what you are looking for is Fuse 60 in the smaller front fuse/relay box under the hood. Should be 15A