The way to go on things when they are totally confusing is to pick one item and find a cure for that and as you go along, you will often find one cure may fix several things.
Your RV has three systems for electrical. Most of what you mention are in the "Normal" car/truck section, so it needs a look just as you would on any car or truck! That cuts confusion as you don't need to worry about all the other things like the power cord, generator, inside lights,etc. Just think about the stuff a truck would have!
Then cut the chase again by disconnecting anything from the trailer plug on back. That's lets you test just the RV.
There are several things that may need more thought to help clear them. One is the brake lights. There are often two sections/filiments in the brake light bulbs. One which is the taillight and the other which comes on when braking. But they are easy to confuse as they are in the same bulb!
I might first startlooking atobvious things like the wiring to the plug on back if there is still a problem with the cord disconnected.
One problem is that you have not told us much about WHICH 2006 Itasca you might have and there are lots and lots of them, so maybe take alook at this list and find which you have as a way to start looking for drawings and info if we need it?
https://www.winnebago.com/Files/File...ram/Wiring.htm
Do you have a meter to help sort out when you have 12VDC and ground at different points? It's very hard to work this problem without the right tools!
If you have a meter, try testing for good solid ground on the correct pin in the plug on the RV back.
I think this will be what you have:
While there,look it and the wiring over. Does it look like there is enough corrosion to cross between the pins? Is the wiring feeding it okay or is it mashed insulation falling off, etc?
Many of the problems you've mentioned can come fromthe wires getting mashed together and a good place for that is where the trailerplug hangs down and get drug around on the ground! They are also hanging out in about the worst weather in the world!
Do a little checking and get back to us with more info and we can begin to sort it a bit??