I am trying to figure out my trailers electrical system, specifically the 12 volt side of it. At this time nothing works even if the tow vehicle is hooked up. That might be because when I open the battery box, this is what I find...

I had read in a search that there was a fuse box under the front behind an access hatch. I removed the hatch and found this along with another snake skin....

I pulled all that out and now I scratch my head at what all this is....

I also scratch my head over what is what in the box by my rear vent. I would like to put in a fantastic fan, but when I open the cover I find this...

I should say that everything works on the 120 volt side, or did until I removed the circuit box. I want to put in a converter and batteries. Will I be able to power up the 12 volt by jumping off of the feed on a light fixture?
Any help would be great.