I connected the light green wire from the harness in the trunk to the rs backup lights, but no power. Any ideas?

Did you have the key on, and trans in reverse? Is the shifter original? Is it a column or a floor shift. Check the reverse switch (should have a pink and light green wires) Pink should have power anytime key is in on position. operate switch manually, or jumper the pink to the light green, backup lights should light. This will tell you if you have a switch problem (bad or out of adjustment) or a wiring problem.

It seems strange that only one wire goes to (or from) the light fixture. I guess it grounds itself?

Got it to work