I’ll try to document adding signals/blinkers/ or perhaps the best discription “winkers”.  Never done this and will likely need some help along the way ,
 For background it’s a1970 AT 125 and in the parts bin is wiring harness and lights from a CT  

Check your AT harness... it probably has provisions for the signals already.. Just need to plug in the switch and the lights.

Dark Green & Dark Brown if there--& spare.

 Quick check tonight under the seat and yes wires are there at the rear fender location. That’s pretty cool that Yamaha thought they might be needed. 
 

So my question is similar. I have both a 71 AT-1C and a 71 CT-1C, and both have come to me with turn signals (AT) or having had turn signals that were removed (CT). Neither worked. The wires don"t mate up color-wise. So I cannot depend on either PO.
I just need to know what color to what color, and my wire diagrams are not helping me much. The CT has Blue, Yellow, and black coming out of the tail light, and I find the Blue and Yellow in the harness, but then there is a black and a brown and a dark green out of the harness. Am I correct in assuming the black goes to Black and the Dark Green and Brown once served the turn signals? And could again?
The AT is a little more complicated. Out of the taillight bundle come the same Blue, Yellow and Black wires, which I assume mate up with the blue, yellow and black harness wires. And the harness has a Brown and a Green wire, but the wires leaving the turn signals are White/Red stripe with a Black collar.on the right side and Black/no stripe with a Dark Green collar on the left side. Do these collars indicate the true colors of those wires? Is the Black collar supposed to have been Brown? Can't imagine it goes to ground/earth but must plug into the Brown harness wire. Also, the Black is receiving the Black wire from the tail light, no? So Green left, Black (should be Brown) right?
Electron gurus?

"Am I correct in assuming the black goes to Black and the Dark Green and Brown once served the turn signals? And could again?"  Yes.

Do you have a continuity tester?  On the turn signals with the strange wires and bands You'll want to connect the Dark Green and Dark Brown wires coming out of the harness to the wire into the respective turn signal (left or right) that goes to the center terminal of the bulb...  take lens off and remove bulb use one probe of tester to terminal in center of bulb socket and then see which of the two wires coming out of the light assembly go to that terminal.  That wires goes to harness and other wire to ground. 

Sometimes you get lucky and can actually see which wire goes where after removing the lens and bulb.  Of course then you don't need a tester. 

Thanks, Mark. Should have known it would be you who would jump in first with good info. After all these months.
This time around I have been gone so long with some health issues. I've had 3 MRIs (brain, spine, and pelvis), a colonoscopy and endoscopy, a problematic foods study, a tilt table study by a cardiologist, and tomorrow night, a sleep study. Thus far, no one can tell me anything's wrong with me. Getting in some good bike work, though. Could be/should be back on here more regularly.
Thanks!

You're very welcome Jim.  Take care.  I know how the health thing can be.

Trying to think what to say without saying the wrong thing so just Wow, sounds like ya getting the good treatment even if it comes up a blank. Good to have you back!!.

Thanks, RT325. Closest anyone can come is one of the many neuropathies. Nothing life threatening...yet. Nice to have three MRIs come out clean, and the gastrointestinal films be without problems.