<a href="https://ibb.co/HfYpm1sn"><img style="max-width:100%;" src="https://i.ibb.co/W4FpSqwg/horn1.jpg" border=0></a>

Sometime ago, I posted a picture of me riding my 250 Ossa for the first time, along with something like "just the horn and brake light to do". Well, I can't.
The generator (no battery) has 5 wires - 2 to the coil, and 3 more (red, green and brown). The red powers the lights, but passes through the horn. (see photo).
The green also passes through the horn. As far as I can work out, the brown is just for the brake light. It (the horn) surely must work through earthing to the frame via the button on the handlebar, but why on earth (pun intended) would it need 2 power supplies? I have several wiring diagrams from the net, but none match my bike...