Hello Jeff,
The conduit full of cables, as you no doubt surmised is the masthead and steaming lights.
The other end of this was next to the bulkhead on in the shower cabinet. It's too full to use, and when I replaced my mast wire runs, those wires would not budge. More on that in a minute.
I think the empty one goes to behind the starboard companionway vent (or instrument). I couldn't use it, and (perhaps unwisely?) just ran the cables carefully in the ceiling void. From there, I had an unused conduit that went to behind the nav station, right next to the bulkhead. Now that I'm thinking about this, I seem to recall it is the same conduit, but broken open there next to the companionway, where it makes a sharp turn. Not sure what happened with it, but I would suggest removing what's there and having a peek.
Related, I went to replace the final segment of coax for the vhf. This is the one between the radio and the base of the mast. Imagine my dismay when I found the conduit for the coax, had a casual cable staple, preventing the cable from moving, approximately a third of the way through the run.