Welcome to the forums. You have received a very nice inheritance, one that will last for many years and fill those years with fum and pleasure. What a great way to remember the thoughtful loved one you you inherited the trailer from.
Now you need to get that nasty electrical nuisance fixed. Lew put you on the right track. If you do not own a volt meter as well as a needle tester now is the time to purchase them and learn their use. A good meter will cost you under $20.00 bucks and will give you amps, volts and resistance. A needle probe is under $10.00. Both these items live in my tool box and travel with us on each trip. Hopefully you will find the problem at a connection such as a light or electrical outlet, 120 or 12V
. Does everything work? All lights turn on, power to all outlets, fans, refrigerator, clock, control panel. If something is not working that might be a good place to start looking. Remember that your trailer is built with two aluminum shells one on the inside and one on the outside, these are connected by aluminum ribs. You do not feel the shock inside because of the vinyl covering on the panels.
Good luck to you and keep asking if you can not find the source of this "current" leak. Let us know what you have done and maybe someone will come up with more suggestions.