1979 Kawasaki Z1000 MK2 A3A electrical issues

Gents, and ladies if any frequent this forum, I'm stumped!

As noted in a previous post, I have all the idiot lights working, headlight, indicators and brake lights work, but I still can't get the horn, passing beam, or go button to work.

All wires are connected, except a black one from the left handlebar control which doesn't seem to have a home that I can find. 

I'm using the A3 European spec wiring diagramme as shown in the photo, but can't seem to find out where I'm going wrong.

For context, the OEM wiring harness and handlebar controls are installed, the battery is both new and fully charged.

Any thoughts, hive mind?

Are they OEM controls of emgo?

Missing ground to the controls and handle bar?

Go button?
Do you have a meter?

Not sure about go button either?  Will say the horn button is the ground source for the horn. I would also ask what sort of end/connector is on the end of the black lead that appears to have nowhere to go?

By go button, I suspect he means the starter button.

If so, then a lack of ground through he bar seems likely. If the handlebar has recently been painted or is an aftermarket bar, then the switchgear may not be getting a proper ground connection through the bar as intended.

The only black wires from the left handlebar control are the two from the clutch switch. one should go to the black from the right handlebar switch and the other to the starter solenoid. If either is disconnected, then the "Go" button isn't going to work. The horn fault is the only "ground" relevant fault ref handlebar switch. Check voltages ref the below

 

OEM