The outlet is 120V AC, and the ceiling lights are all 12V
DC, on different circuits with different guage wire. The 120V wires are bigger and stiffer, like in your house, and the 12V
wires smaller and less stiff, like in your car. That should help you sort those out. Look again at your wiring diagram and see if any of the 12V
wires (if there are any) match any of the colors in the diagram. Then use a 12V test-light to see if the one that is supposed to be hot is in fact hot. Go from there...