New Moto Guzzi Door Mats Available Now
Something like this? Turn it around so that the button faces forward. Wire one lead to a switched power source and the other to one of the horn terminals. Other terminal to ground. I prefer these Fiamm horns. Sometimes I use both a low tone and a high tone horn together.https://www.amazon.com/JFG-RACING-Universal-Motorcycle-Backplate/dp/B07CK2RBP5/ref=asc_df_B07CK2RBP5/?tag=hyprod-20&linkCode=df0&hvadid=312195936700&hvpos=&hvnetw=g&hvrand=1653775820877833425&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9002126&hvtargid=pla-569439188070&psc=1 https://www.amazon.com/FIAMM-72112-Freeway-Blaster-Note/dp/B000DINKPQ?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=ATVPDKIKX0DER
Or you could re wire the flash to pass headlight switch that seems like is in the perfect position. If you have a modern bike that is.
Since you are missing your left thumb, maybe a better solution is to switch the functions of the start button and the horn button. That should be pretty straightforward.I feel your pain, since I’ve only got one and a half thumbs myself.