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!)
Baron, Julie, Lil' Barry, Faith and OSD, Fang
'03 Hyundai Starex(H1) 2012 Coachmen Clipper Sport 126
Incheon, S. Korea
From six months of no camping to having a winter site 30 minutes from a ski resort! I'm a happy camper!