Tradewind has two separate electrical systems, one that is 12 volts direct current (DC) and another that is 120 volts alternating current (AC). The 12 volt
DC system operates off a 12 volt
battery. The 120 volt AC system operates when you plug the trailer into a "city" outlet whether at home, in a trailer park, or somewhere else.
I can't help you with most questions. But picture #2 shows the switch, probably for the fan, that lets it operate either off 12 volts DC ("Battery Power") or 120 volts AC ("City Power"). It can operte on either current, but not at the same time.
Your original light fixtures will have 2 Edison type screw in sockets for light bulbs. One side operates on 12 volts DC and the other on 120 volts AC. RV stores sell house-hold size light bulbs that operate off 12 volts DC. If you mistakenly scew one into the 120 volt AC socket, you will get a bright but short-lived flash of light.
Use regular low wattage household light bulbs for the 120 volt AC light sockets.
A digital multimeter (VOM to us older guys) will help you identify your electrical circuits and outlets. Just remember, Redi Kilowatt runs half of your tailer. Have fun!