Wiring Harness Nightmare

Installed a plug and play wiring harness on my 2008 Tacoma. The trailers brake lights and signals work when lights are off. When I turn on the headlights on nothing works, running, tail, brake signal. Any ideas how to trouble shoot this? This is my second kit, as I assumed my first Curt harness was faulty.

 

Are you talking about a plug n’ play trailer tow harness?
Where did you “plug” the harness in? Rear tail light?

 

I'm assuming he means this.
https://www.curtmfg.com/part/55513

I'd want to check things at the plug itself first of all before hooking up a trailer.

 

Oh, yeah.
I vaguely remember another member here not getting the Ground wire for the box grounded good.
It did some weird stuff. Maybe start there AFTER you see what you get at the 4-way plug.

 

It’s a Curt MFG wiring harness. It connects directly into the rear tail lights. After assuming the converter was bad I replaced it. Now, I even brought it down to my local U-Haul and they are
just as stumped. Went through the
grounding wires as the frame was replaced. All seem to be in good shape.

 

when you say nothing works, do you mean on the towing harness or now your tail lights on the truck don’t work either?