Usually on trailers the large white wire (10 ga.) is the ground, and the large black wire (10 ga.) is the main power.
You NEED TO put an in-line fuse between the battery/main hot lead and the power outlet, and between the battery/main hot lead and the interior lights. My guess for fuses would be 5 amps for the power outlet, and 10 for the interior lights.
Solder and shrink-wrap the connections you make. Those clip-on connectors are worthless for high amperage connections.

You DON'T want this... (This is brand-new from the factory!)
