If you don't use the trailer hitch, at this time. I would suggest just getting rid of that cluster %*#. Looks like someone just hacked it in. I hate those quick splice connectors, as they almost always cause corrosion, with time. I believe, that you should really solder and heat shrink all connections.
Also, the relays under the hood could have been added, for example, for lights that were installed, or any other add on electrical device.

You may want to go around and check, easily accessible, factory connections. See if the rest of the connectors and connections are sound. This include grounds. I'm assuming that you may know a bit about wiring from what you wrote. If not just ask, many here are willing to help.

I would rip out anything that was added and start with what was originally installed on the vehicle at the factory. If you are unsure what was added, and you know it has defective wiring, disconnect it for now. Then get a Service Manual for your year vehicle and learn how to read, at least a basic, wiring diagram.

It would seem you have a real project on your hands.