Thanks Mr. Jack. What confussed me was that I only have 1 yellow wire coming out of my trailer wall. There is a light switch which operates it underneath my cabinet upon entering the trailer. So I guessed that the light grounded to itself. That was why I did not have a white wire coming out of the trailer wall.
Sorry I confused you. The yellow wire coming out of the wall is the power wire. It comes from your switch. You will attach your new black wire to it with a wire nut.
The electricity returns to the battery (the ground side of the circuit) through the trailer's frame. You connect your white wire to a screw, and this is then screwed into the side of your trailer, into the metal frame, which completes the circuit.
Hope I haven't confused you more with this.
- Jack