How do you fix the horn in a Toyota starlet?

On mine, the spring-loaded button in the steering column had worn down so it was no longer making contact. I very carefully took an spent .22 shell and slipped it over the button. This worked even though it was a tight squeeze reaching into the area. You have to remove the plastic housing around the steering column to access this area. It's only a couple of screws. The spring-loaded button constantly rides up against the steering wheel center area, so it's always making contact and hence wearing down. I hope this helps you. Maybe another similar shaped object would work, but the spent .22 shell is the best I could find. It's the perfect fit.