But the tail lights/marker lights/running lights don't have anything to do with the turn signals and brake lights. Those are the same circuit on the left and right, as are the brake lights.
The problem arises as a result of the US habit of using the brake light on one side as the turn signal, which European cars tend not to do. The turn signals are separate lights. If you don't use a diode setup (commonly packed into one of those 5-to-4 wire adaptor boxes) then you effectively connect your left and right turn signals together, along with your brake lights.

 

I'm renting a trailer again on Wednesday, I'll try to get you a video.

 

With that said, I'm still unsure of which wires, sides, and colors I should be looking for. As there is No factory trailer harness connector anywhere on my 04, not in either tail light or underneathe it.

 

Remove passenger tailight, there is a connector attached to the body 1/4 panel on the outer most panel below the headlight.

The OEM harness comes in 2 parts, one that hooks to said connector that I believe has the little box and the other runs from box to plug at hitch.

I have the first part of the harness I can sell if that helps you any.

 

I found it. I'm an idiot, I don't know how I didn't see the harness the last time I took the tail light out.

Yes, I'm interested in the harness you have.
Which one do you have? How much?
Thank you

 

i only have the box portion in this pic with 2 grey connectors. not sure you can make it work with just that.

 

I'm just going to buy a new complete harness.
That way I'm sure it's right, and has what I need.
Thanks for the offer.

 

Good idea