How to connect this wiring?

Here is an easy to follow 4 pin trailer wiring diagram. A new harness and this diagram would make for a much better final product.

You are probably going to blow a fuse in the truck doing it as you are proceeding. Have extra fuses on hand or for less than the cost of fuses, buy a test light. They are $2.
Turn your lights on in the truck and probe with the test light to see which wire now has power. Connect that to the brown wires leading underneath the trailer. You should have tail and clearance lights. If not, you have a cross-wired trailer wiring schedule and should buy a harness and start over.

Thanks. Last night I connect the loose cable on the side(yellow light) to the light and tried it to the frame. Did nothing. Started to rain so I had to stop. Tonight I plan to connect the loose brown cable by the hitch, double it up with the other brown cable and connect both the the brown cable. (sounds confusing right? :) )
Hoping that will solve some issues. Not sure I'm ready to rewire the entire thing. Mainly because I'm not sure what I am doing.
I'll report back.
Thanks for the patience with me.

Those amber lights and the tail lights (headlights on) should be powered by the brown wire.

A test light or meter helps this process quite a bit.
As was mentioned, good suggestion to buy a new harness for $15 and wire it all correctly to the proper schedule.

Etrailer harness

Crawling around under a trailer is not a lot of fun, especially for old guys like me who don't bend and stoop like I use to.

If it is only the tail lights that are not working, I would start at the tail light assembly(s). Locate the wire for the tail light on each side and trace them back until you reach the front of the trailer. Then you can determine where, or if, they are connected. Then you will know which wires to be troubleshooting.

Thanks guys. I'm getting a little confused. Sounds like I might need to start at the yellow side light. Should it be a ground or should it attach to the yellow side light? Once I do that I will see what works. But if nothing changes then I am confused at what to do with the brown wire.
I will work on it this evening and trace a few things out.

Thanks

Locate the brown wire that is spliced to the white. White should be ground. The brown wire connected to it maybe going to the taillight fixture as power lead.

That yellow side light probably only has one wire for power and uses the frame for ground. The wire hanging loose is probably not used, at least for that light.

Even if the "repair place" were next door, I would not take it back to them. That looks like one heck of a mess. It would bug me so much I would just go buy a new trailer harness assembly, rip out that mess that is there, and rewire the whole trailer. In the future when you have problems with one of the lights (and at some point in time you will if you keep it long enough) and have to troubleshoot it, you will appreciate having it wired properly and the color code correct.

Thanks guys. OK, I took some closer pictures. Drivers side yellow light has a cable that is not connected. I will hopefully have time to connect this tonight.

When the truck is connected to the trailer; both turn signals work and both sides work when the brake is applied. When my headlights are on, NEITHER rear light works. I should be able to figure out where the one cable will connect to the yellow side light. I'm thinking I should hook up the side light and see where that gets me. Do you think the not connected brown cable isn't needed because there is already a brown cable connected from the truck to the hitch?

I can email you a picture of the hitch part if you need to see a closer image.
Thanks!!