If you have the old style large frame mounted horns, they have a set of contact points inside that will smoke if they are in need of cleaning.
I rebuilt mine as the Horn Guy in Beloit Wisconson couldnt do them, he has no parts. Take them off the car, take the cans off, and clean the
points with a VERY FINE file, like the kind one used to use on ignition points. If you dont have that, use some 220 sandpaper.
Put some lube (NOT WD 40!) around the electromagnet, and let it sit a day or two. When you hook up 12V to the horn, the points may smoke a little at first, but should not after that initial test. Now for the tricky part, there is a adjustment nut, if the horn doesnt sound right or is silent
adjust this nut to move the points closer together, DONT TURN IT MORE THAN ABOUT 1/10th OF A TURN! This adjustment is critical!
When the horn sounds OK...LOUD
I use a jam nut to securely lock that setting in. The nut originally had a locking device on it, like a
nylon insert, but once the nut is moved, this is pretty much useless...thus the jam nut. When you get both horns "tuned", this is my favorite part...hook them both up and ask your wife or girlfriend, or both, to come see what you did, hopefully it will be in a small room.
I love those old horns! Good luck!