Yep MarkT's the Man & put a hell of a lot of time & thought into it.
Me--we--rest of us--possibly trying to keep out.
If you seperated the two black, where do they go to now [to where Mark said?]

re 'headlight and gauge lights' disregard if I missed something in earlier replies.

I had same problem with a vape and a '78 DT 125 - stock the '78 had three wires from the OEM magneto - B/W to coil, Y to turn signal switch in headlight bucket, and G/W to rectifier. Yesterday, I ran a wire from the positive vape / battery connection to the yellow wire at the no longer used OEM connector in the harness. Lights work fine now.

This bike did not have an on/off for the headlight, but the wiring diagram shows that the power for the light, and the illumination lights for the gauges, bypassed the ignition switch.

OTBMF, If as you say your bike did not have an on-off switch for the headlight, and you connected the yellow to the battery, your headlight would be on constantly...  24/7.  Until the battery goes dead. 

If you have a headlight on-off switch, then with yellow connected to battery you will need to always remember to shut off the headlight switch when you park, or again, battery will go dead.  This is a workable choice.

To me, the far more "elegant" solution is to wire a VAPE-equipped bike as original...  where the headlight comes on with the engine only.  But that certainly isn't the only way to wire it. 

 

Want to thank @markt for the explanations here with this issue. The instructions that came with the vape were unclear when it came to the lighting circuit. Both myself and my aerospace engineer uncle and I knew something wasn't right but could not figure out what... Until I read this post. Worked like a charm first try. Thank you for saving me hours of head scratching with regard to the two green wires. 

You're very welcome, glad it helped!