So, here's a point of high strangeness. I couldn't get any change in continuity readings by wiggling the length of the wiring harness. Ends of wires and plugs also looked good. So I decided to unwrap the harness, and found this splice in the middle of the red/blue wire under the tank. This is not in my schematic at all. Here's what I know:
1) One brown/white wire feeds into the left front turn signal and splits to the speedo.
2) Other brown/white wire feeds into the tachometer plug.
3) Tach plug has heat discoloration at the brown/white wire.
4) Blue wire at the splice feeds into the right front turn signal.
5) Someone installed aftermarket front turn signals at some point.
6) When I unplug the bullet connectors just south of the turn signals, I get open lead reading in the red/blue wire.
So...it seems to me that whoever installed the front turn signals also did the splice, and when the ignition switch is turned on, that circuit is getting power from both ends and causing excess voltage/heat, thus blowing the turn signal fuse at the end of the red/blue wire.Unless someone foresees a major explosion or catastrophic meltdown, I'm planning to cut out that splice in the red/blue wire, return the turn signal circuit to factory schematic, and see what happens. I may have some gremlins in my instrument clusters to track down, but at least I'll hopefully be starting with more knowns than unknowns.Any insights or confirmations appreciated.