First off let me say I haven't read through this post, but your last post sounds similar to a problem I had. I far as I know it's not a common one, but a real pain to find.
My symptoms, headlights out, city lights out, same buzzing, blinkers not working but all burned steady & very dim, high beam indicator & signal indicator stayed on. Don't remember about the cluster.
I ended up finding a ground block in the harness corroded up. There are 11 of these blocks thru out the harness best I can remember. You can feel small rectangles in the harness, 1/2" or so.
My bad one was right near the air filter access. I cut it out & soldered the wires together & put a wire nut on it. That's been probably 60,000 miles now with no more trouble.
I would post a picture of it but haven't figured out the pictures here.
I will look at that first when I rip the plastic off this weekend. Thanks for the post.
Sometimes electrical troubleshooting is similar to attempting to find a black cat in a room with the lights off, all the time while wearing oven mitts. I've located electrical/electronic faults in power plants the size of a city block - easy. This one is sitting right in front of me and laughing its ass off.