New 20 ounce tumblers available now! Forum donation credit with purchase. https://www.wildguzzi.com/Products/products.htm#Tumbler
My '87 SP II has a toggle switch in about the same location and operates the hazard lights/flashers. Came from the factory that way but I'm not sure if earlier SPs had a similar setup.
You might try here for a manual for the bike that might help a bit on figuring out what wire went where here:http://www.thisoldtractor.com/moto_guzzi_tonti_workshop_manuals___shop_manuals___service_manuals.htmlMight scrounge around a bit as there could be a simple to read wiring diagram as well.Good luck!!Tom