[SpudRider]

There must be two wires leading to the horn button. One wire supplies power to the horn switch, and the other wire transfers this power to the horn when the horn button is depressed.

Try this experiment. Connect the light green wire to the positive terminal of a power source, which can be a motorcycle battery, or even a 9V dry cell. Connect the dark green wire to one of the spade connectors on the horn. Finally, connect the other spade connector of the horn to the negative terminal of the power source. Then press the horn button, and see if it the horn works.