If they dont work there is a pretty easy way to fix them. They usually dont work because the contact points inside have welded together.
1) Unscrew and remove the little adjusting knob/bolt. Once it's out, spray the inside of the horn with a bunch of penetrating oil through the tiny hole adjuster bolt hole. Then replace the adjuster knob/bolt but not too far in as this is the adjustment on the contact points.
2) Get a couple alligator clips and a battery charger. Hook the positive lead to the main terminal and the negative lead to the bracket. Set the charger on the medium setting.
3) Place the horn on a wooden block against on the floor. Get a hammer and whap the bracket of the horn several times. After a few hits the horn should start blasting louder and louder.
