Nate, thanks so much ! I always love to see naked pictures of mechanical things , and the find at my next door (to the car, not me) Texas shop is terrific--even the Alfa guys don't seem to carry the part (and amazing that even at Re-originals there is no attribution to whatever car it would go on…).
Steve, believe it or not I went to work humming to ZZ Top's Blue Jean blues, '..if I ever get back my pickle jar, Lord, how happy could one man be...." But fyi, the "15/54" seems to be the designation for the terminal...Here from the original schematic;
[update November 2022; The numbers in the schematic are DIN 72552 references, https://en.wikipedia.org/wiki/DIN_72552 . The "INT" designator isn't defined, but probably means "Ignition" and provides a dedicated contact for the Coil...At least, preserving an isolated contact to keep the car running is probably a smart choice. Otherwise, its pretty simple; Terminal 30 is the input from the battery/alternator, 50 is to the starter solenoid, and everything else is connected in Run. Older switches and older definition distinguished a "16" terminal instead of the "15" terminal, either function as the hot wire to the coil and seem to do the same thing as the INT terminal. The 15/54 essentially means "everything, both #15 class circuits (ignition) and #54 (kitchen sink of lights or whatever).
Nate clued me in a long time ago, Italian motorcycles had nearly the same switch, but (maybe except for Moto Guzzi) no "start" position (only 2 positions). Those switches are the Q149 series.]
Now, what does " Avviam" mean ? Lee