Actually Mike, I've been super busy so I haven't gotten much done on it lately, but I'm taking your suggestion and moving all the tail light (& rear turn signal) wiring over the fender & under the seat. I'll post a picture or two soon.
Briefly, I disconnected the harness and pulled it out from the metal loops on the inner rim of the fender, then ran the two wires from the tail light through the loop closest to the light (to hold them in place) & thence up over the fender rim and into the connectors on the harness, now located above the fender.
The two bullet tail light wires now simply go over the fender to where they connect to the harness.
The harness itself is not actually on top of the fender; I've attached it to the fender rail using zip ties. Surprisingly, my biggest problem was dealing with the excess slack in the harness -- after moving it, it was more than a foot too long. I coiled up and zip-tied the excess & tucked it under the regulators.
My rear lights ground to the fender/frame itself, and sometimes it's hard to get a good connection trhough just the mounting bolts. I added an "extra" ground connection for all of them -- ring terminals on the mounting bolts, running back to the ground wire of the harness, and all of these bolted to a new hole in the top of the fender, pretty far forwards so it'll be hidden by the seat.