Welcome to the forum. We feel your pain. My advice to anyone buying an RV is to be handy with tools or a check book. These things live on an earthquake fault and something is always loose or broken.
That said, there is no excuse for poor workmanship and it seems to have been in every RV I have ever bought.
If you don't have a voltmeter, get one and watch some you tubes to get confident. Buy a 12 volt test light and learn how to use it.
Now the really difficult one. Understanding your entertainment systems can be intimidating and just downright miserable. There is a lot to learn. Switches, splitters, coax's etc. What can work, what does work, and where the heck does that cable go?
I will recommend an inexpensive tool in a minute. You need to get some labels at home depot that have numbers on them or a nice dymo label maker.
Take some pictures of your wiring and if you have a decent owners manual, copy any diagrams that are in there. Print the pictures and diagrams out so you can write on them. I promise you, you will not remember what wire goes where in a week.
You need to know things like a coax being a end run. That is, nothing at all between each end of the cable. You need to know where they might have hidden splitters.
You need to understand your roof antenna and how it works and when you have park cable how to turn the roof antenna off so it does not interfere.
I cannot count how many hours I have spent in my RV cabinets chasing wires and changing things. I guarantee I have spent 100 hours in the last 8 years.
So don't get discouraged if you haven't sorted things out in a year. Rving is a hobby as well as lifestyle.
You really need one of these. They make finding blown fuses much easier.
Do read your manual and take notes and use a highlighter. Go back again every few weeks until you are confident you can find things when needed.