Lisa, I'm pretty sure the white wires are ground wires and the green ones are the positive 12V feeds. Was that light just a running light, or did it combine stop and turn signals too? If you don't know, hook your trailer up to your tow vehicle and see what the upper left light does.
If it's just a running light, then your original must have had two separate bulbs and they had separate feeds. You can just splice the two white wires from the trailer together and connect them to the new light's ground. Splice the two green wires and connect them to the new +12V feed wire on the light. You could use wire nuts that are big enough to accept three wires each to do this.
IF, however, you had stop and turn signals there, you will need to find a replacement that gives you the same function. And, I don't know where you'd find one in that shape and size. You may have to mount a different kind of light there, filling the original holes with caulk, or covering them with fiberglass or even Eternabond tape.
If I'm not making sense, just tell me what you don't understand and I'll try to be more clear.
- Jack