Hello, while Im trying to solve the alternator problem from the other post, this just came up last night and I think it is more important:

OK, 1978 Fleetwood, it is kept outside for now, and last night here in IL it got down to about 20 degrees, not sure if that matters but at about 5 am I woke up to the sound of my horn continuously blowing. I ran outside and for some reason the horn was just blowing by itself. I didn't want to try and fix it then, I just wanted it off! I ran back in and by the time I grabbed some needle nose pliers and the manual to see which fuse runs it, two of the four notes have stopped making sound, and only the real high note and middle-low note are blowing. So I quickly pull the 30amp fuse that runs the horn, seats and windows. So the horn stops blaring, and by this time two neighbors are awake and a dog is barking. My dad was also convinced that I added some sort of "aftermarket horn" because he couldn't believe how loud it was, but I told him that's what Cadillac horns sounded like in the 70's!! OK, later in the day, it has warmed up a little and I talk to my neighbor who says it was on for at least 10 minutes before that and I apologized. Now, I carefully put the fuse back in and it is not blowing by itself, so that is good. Now, when I went to blow it, only ONE note worked, the real high pitched one. I start the car, and two work, real high and mid-low. I turn the car off, both work for about a minute, then back to just the high one.

So, as far is blowing by itself: First, I called a couple friends and two told me that it was possible that the horn pad shrunk due to the extreme coldness, causing the horn to blow. Well as of now, this is all I have to believe.

But the bigger problem is how do I fix these horns so that all work again? Tomorrow, I am going to take them all off and put battery grease on all the green wire connections, tighten the bolts so they are grounding right, and re-seat the fuse. If that doesn't work, I guess I'll have to buy new horns. My friends also said that is might have been possible to "blow out" the horns or they got too hot from being on for over 10 minutes. My last thought is that it could be the horn relay, where is that located and what does it look like? Any help appreciated, thank you.

From the FSM:

Horn blows constantly:

1. This can be caused by sticking horn contacts in the relay or horn pad.
2. Horn relay may be energized by grounded or shorted wiring.

Burned open windings on most horns are caused by one of the above malfunctions. Before horns with open windings are replaced by new horns, make sure that none of the above conditions exist, or the horn windings will again burn open.

Bench Checks:

1. Measure current draw of horn while horn is operating. Current draw for each horn should be bewteen 4.5 and 5.5 amperes at 11.5 to 12.5 volts.
2. No current may indicate a broken connection or an open circuit due to a broken lead or to overheating. Most horn problems are caused by horns being operated continuously, which develops sufficient heat to melt the wires in the winding, causing a open circuit. Overheating is accompanied by a characteristic odor which indicates that horn has overheated and should be replaced.
3. No current can also indicate that the contact points are open and a current adjustment is required. Turn adjustment screw counterclockwise.
4. High current, over 20 amperes, indicates an overheated winding or shorted horn which should be replaced.
5. A reading of approximately 18 amperes for a 12 volt horn indicates a condition in which the contact points are not opening. A current adjustment is required by turning the adjustment screw clockwise.

***
The horn relay is located in the relay panel, which on the driver's side of the instrument panel to the left of the main fuse block. The horn relay is the squarish one just above the key warning buzzer, which is on the very bottom of the relay panel.

Hope all this helps, and if it makes you feel better, you may have found the electrical short causing the problems cited in your other post.

Craig

A friend of mine told me this happened to his Camaro once - while he was driving! After 10-20 minutes the horns started smoking and they definitely blew out.