greg bender
http://www.thisoldtractor.com/gtbender
I extracted this information from Leon Karlak off of the Yahoo! Loopframe_Guzzi news group.
Any 22 mm or 7/8" handlebar switch can be fitted, but period correct switches are more difficult to find. Fortunately, Yamaha still has a nice unit available. Drop by your local Yamaha dealer and pick up part number 396-83972-11-00 (YHA205). This switch was originally fitted to the 1970's RD 125.
Charles Hamer was kind enough to send me the wiring code cross-reference to make installation on our V700, Ambassador, and Eldorado models quick and easy.

Yamaha handlebar switch YHA205 / YHA 205 / YHA-205
| Function | Yamaha YHA 205 | Moto Guzzi |
|---|---|---|
| Horn (wire to distribution panel) | Beige | Black |
| Right turn signal / turn indicator | Brown & White | Yellow |
| Turn signal / turn indicator (live wire from fuse panel; goes through flasher unit / blinker unit) | Black | Purple |
| Left turn signal / turn indicator | Dark Green | Yellow & Black |
| Running lights / parking lights (tail light, gauge illumination lights, etc.) | Blue | Red & Gray |
| Headlight high beam | Yellow | Green & Black |
| Live wire from fuse panel | Red & Yellow (can be faded, look close) | Brown |
| Headlight low beam | Green | Green |