Since a picture is worth a thousand words....
You can see the green and white pair taped together that runs up to the upper marker lights...
marker lights 2 by
gijoecam, on Flickr
Those two wires go down through the floor into this rat's nest:
marker lights 3 by
gijoecam, on Flickr
Those two wires join up with two other wires which come from the rear.
marker lights 3 by
gijoecam, on Flickr
The white ground wires appear to run all the way back up to the junction box I was in yesterday. Those were the two ground wires I cleaned up yesterday, but they're not part of the problem. Incidentally, I found the wad of ground wires mounted to the frame rail dead between the axles (about the most INconvenient place to work on them should the need ever arise!)
marker lights 4 by
gijoecam, on Flickr
Here you can see the bundle of four wires for the marker lights pulled out of their split loom. They come from the junction box up front, enter the camper at some point, cross over the wheel well, and go down through the hole under the fridge, split with one pair going rearward, then one pair going back up through the same hole to the upper marker lights.
Here's where they run in the fridge access:
marker lights 6 by
gijoecam, on Flickr
marker lights 7 by
gijoecam, on Flickr
At the top, I can see where they turn and go into the chase, but I'm not ready to yank the vent grate off the roof skin just yet...
So that's my saga in photos thus far... Thanks for the moral support gang!