Modern Vespa

For the DIY guys:
1 You need 2 6V stators.
2 Each stator has 3 coils: an ignition coil next to the points and 2 lighting coils.
3 Sometimes the ignition coil is connected to one lighting coil with a yellow wire. Cut the wire and ground the wire coming from the ignition coil
4 Remove that lighting coil (the one with the thick windings).
5 From the second stator, remove the lighting coil with the thin windings. It has a blue and yellow wire. Fit that on the first stator, ensuring that the blue wires of both lighting coils are on the left or right, not next to each other.
6 Ground the yellow wires coming from these coils.
7 Connect the two blue wires at the connecting block.
8 You will now have 3 wires coming from the stator: black = earth, red = ignition and blue for the lighting, brake light and horn

The lighting coils with the thin windings and blue and yellow wires produce more than 25V. But they must be connected in parallel, NOT in series. Now all you need is a voltage regulator with 3 connections, and you have 12V AC.

Please note that your wiring must be modified after the 12V conversion.

Is there an advantage to doing this over just getting a 12v conversion kit like the Vespower?

No, it is purely for costsaving purposes and for those of us who like to tinker around.