Horn not working

I think I am making this more difficult than it needs to be, but my horn is not working.  I do have new bars which were powder coated black, however I have already sanded down the paint for the switch to make contact, no change.  I have a new left switch from z1parts.  Am I hooking it up correctly?  I am using the brown and black wires from the harness to connect to the horn.  

I only get .6 volts when measuring, so I'm thinking I have a grounding problem, because as soon as I measure the brown wire to the negative side of the battery I get 12v.  What can I do here?

I think the black wire should come out of your left switch control.  (Connected to the horn button)  This wire  doesn't connect to the plug on the end of the switch control....it bypasses the plug.

I tried using the black wire coming from the switch, still did nothing. 

Also the horn by itself works, I tested it against the battery. 

The brown wire from the harness connects to the horn and is supposed to provide continuous switched battery positive voltage to the horn.
With the ignition switched ON, could use a voltage meter to assure that battery positive voltage is present at the horn terminal.

The black wire connects to the other horn terminal and goes from the horn to the horn button. Pressing the horn button is supposed to ground the black wire.

The body of the horn itself need not be grounded.

Perhaps the horn button, when pressed, is failing to produce a good ground.
Could attach a separate wire to the horn's ground terminal and touch its other end to the engine in order to assure a ground.

Good Fortune!

Would also assure a good connection where the cable from the battery negative terminal attaches to the rear of the engine.  There may be corrosion that's preventing a good ground connection. 

Good Fortune!

The two wires to the horn are the black wire from the control switch and the brown wire from the harness.  Connect them both to the horn.