I FINALLY FINISHED FIXED ALL THE ELECTRICAL! EVERYTHING WORKS!!!! :clap: :clap: :clap:
Ok, so recap:
1) The original blinker issue was, in fact, the flasher unit. Plain and simple.
2) My dash was pretty badly rusted inside, which was why certain lights weren't working and the speedo, despite having signal at the pin, was reading nothing (it was the circuit board). Ordered a new one, and good to go. Even took apart the donor odometer and set it to the correct mileage.

3) All my other electrical gremlins, though, actually could be traced back to the LED lights the PO put in, but not in the way I thought.
So symptoms were now:
a) both the old and new BMU worked as they should with the new speedometer. Hit both brakes and the light went out. This was especially strange because...
b) my taillight was out. The bulb was good, no indicator on the dash, but I was getting *no* current to the socket unless I jumpered the pins at the BMU, which is why I figured that was the issue
c) my ABS diagnostic was telling me Code 7, aka my computer is messed up. rats.
So the 'aha' moment came tonight when I realized that when I switched the BMU, I still got the same symptoms. Took a look at the pinout diagram and realized that the taillight doesn't get it's power from the 12v source, it gets it from the ignition switch by way of fuse #2.
Checked the incoming wire with a voltmeter and it had *no* voltage. So the issue had to be *upstream* of the BMU. Swapped fuses for #2 and got the same result. Checked the incoming voltage and got *nothing*, but from battery to ground was perfect, so the issue was upstream of the fuse.
Took a look at the ignition switch and noticed one of the wires had been tucked back into the loom. Turns out, that wire *just* powers the tail light and parking light. The guy wanted to run an LED without bothering the BMU, so he jumpered that pin from the 12v and disconnected the wire so the BMU wouldn't have enough current to notice something was wrong.
Coincidentally, that same wire that feeds the taillight also feeds the ABS computer data somehow, so by tampering with it, he had disabled the ABS at the same time. Once it was reconnected and I cleared the codes, I finally got the steady shining LED I had been hoping for.
So I think she's completely good to go now. I haven't let my tank run low enough to check the fuel light yet. I'm hoping it's fine, and I'm not sure I care if I don't. I probably still need to do the fork seals and change some fluids, but that'll be projects for the winter. For now, she's a smooth running flying brick with only 16k on the clock. Time to do some riding!
Thanks again for all your help, everybody. Batman appreciates it.
