Doubt about towing equipment of special trailer.

Hello! Hey, I have a 1981 Ford F100 Ranger Lariat with the Special Trailer Heavy Duty Tow Package. But my question is that in the lower part of the box, there are two connectors with three terminals, I tried one of the connectors and the ground fails, but in the other two terminals there is voltage if I put the chassis ground, I put the turn signals and it worked, but not the parking lights, I don't know if the second connector that I didn't try is for the parking lights, does anyone know how it works or if there is a diagram that explains what the electrical circuit is? I would be very grateful if you could help me solve this doubt.

Take a look here and see if it helps: https://forum.garysgaragemahal.com/Factory-Trailer-Wiring-tp46320p87475.html

Thanks you!Lastly,  I have a connector under the steering column but I don't know what it's for, do you know what it is for?

That's the other end of c1110 though the colors change during its course. You won't need the red/green striped one.

Edit: I should clarify that as it's misleading (aka stated wrong). The red and yellow don't really change. It's just that they are both hot 12v. So different circuits but 'same' function.

I am really grateful to you, thank you!

You bet!
It can be a real mess when looking up under the bed trying to make sense of it.

It can get even worse when a PO tried to 'improve' upon it