Horn Blowing Itself

[MustangFlyer]

In July, I purchased a 71 F100 Explorer Sport Custom and am still in the "getting aquainted" phase of our relationship. Sunday night at 12:15am, the horn started blowing. There's a comical story of me in my skivies at 3 degrees with flashlight in one hand and pistol in the other wondering who was messing with my truck, but that's a side issue. Turns out there was no one there, just the horn blowing by itself. I first disconnected the horn, then went back in and got more clothes on and went back and disconnected the battery. I took another vehicle to work and later in the afternoon at 24 degrees, I returned and hooked it all back up. No uncommanded horn blowing and the system worked as advertised. I know the previous owner so I asked him if that had ever happened to him. He said yes, that it happens any time the temperature drops below about 5 degrees. Now, I (and my neighbors) prefer not to be awakened by a blaring horn, but an intermittant problem can be hard to troubleshoot, and I don't desire to wait until 5 degrees to work on it. Seems to me that something is contracting at extreme temperatures and causing circuit completion. My guesses are either the horn relay or the rubber pad on the steering wheel. I don't yet have maintenance manuals for the truck but I found a wiring diagram here on this site and it looks to me that the relay is powered all the time from the solenoid block and then energized by the horn switch on the steering wheel. That still makes either of those components a possible culprit. I've never heard of a bad horn relay, but that is easier to change than the steering wheel switch, so that's my plan of action. Of course, the only way to test it is to wait until the temp drops again. I found this site in my search for wiring diagrams and decided to join and ask if anyone has heard of a similar problem or has any suggestions.

[TNIceWolf]

MustangFlyer

I had a sort of similar problem with my horn a while back. Now I dont have my horns themselves hooked up so it took me a while to find the problem. What was happening was that my truck kept draining a fairly new battery with an eight year warranty. At only six months old it shouldnt really have been doing that. Anyway I could jump the truck off and everything worked fine. Battery would easily recharge and the truck even ran if I pulled the negative battery cable telling me the alternator was doing its job. About the third time I went to crank it after a day or two of sitting and the battery was dead I noticed that the horn relay was clicking when I hooked the jumper cables up. So I disconnected the relay and guess what? You got it.......no more dead battery. But then I discovered that the relay wasnt faulty per se. What I found was a loose or worn upper bearing in my steering column is flexing just enough in the right spot to make contact in the horn components in the column. Ergo the horns attempt to blow even though they are not connected and the relay is activated. They dont make any sounds of course but the circuit is activated if that makes any sense. Kind of an odd problem for me to encounter but should be a fairly easy fix. This may not be your particular issue but it is an example of what IS possible .

[Racer Z]

The horn blows itself.... I could say something here, but I won't.

Horn relays can and do go bad. I saw to much of that when I was installing car alarms.
I don't know where the horn relay is on the Ford truck, but relays are usually easy to get to. In general, relays are kind of pricey.

I'm glad you mentioned the rubber pad behind the horn ring, cause I never would have thought of it. The cold could be shrinking this rubber that is already smaller than it was 40 years ago. It is very easy to change.
If you have a stock wheel and ring, push the horn ring in and turn counter-clockwise a bit. Then pull pout towards you. Be very very gentle with this. There is a plastic ring with three tabs holding this together. The plastic is brittle and ready to break. The good news is a new plastic is only $5. Turn the horn ring over and take out the three screws.

See this thread for links to new horn rubber and plastic.
http://www.fordification.com/forum/view ... rn#p510725

It never gets cold here and I'm at a loss as to how to test this for cold shrinkage. I hate to suggest replacing one or both blindly.

You are on the right track with the electric flow, relay and horn. Pushing the horn ring completes the ground that pulls down the relay that powers the horn.

[Thunderfoot]

to the site!
The 71-72 horn is different and does have a lot of rubber in it (see pic below for those that haven't seen one) I too think you are on the right track, only thing I can think of to tell if it is the horn pad is if you just barely have to touch it (not much stroke) to blow the horn then this could be the culprit. The relay is easy to change.

[Racer Z]

to the site!
The 71-72 horn is different and does have a lot of rubber in it (see pic below for those that haven't seen one) I too think you are on the right track, only thing I can think of to tell if it is the horn pad is if you just barely have to touch it (not much stroke) to blow the horn then this could be the culprit. The relay is easy to change.

What I described is for the 70 and older. Never had the need to take apart anything newer. Probably much different inside. I missed where you stated the year as 71. Oops.

[fordman]

i vote fo rthe horn pad or the copper contacts inside of the horn pad contracting in the cold and making contact.

[MustangFlyer]

Thanks to everyone for your suggestions. Electrical gremlins can be truly puzzling. I went ahead and changed the relay yesterday. $8 at my local NAPA. Of course, now I have no way to test it until the temps drop low again and it really won't bother me if that doesn't happen. However, I live in MIssouri, east of Kansas City, and our winters have a wide range of temps and weather. I did take apart the old rusty relay last night and it looks brand new inside. I stuck it in the freezer to see what would happen, but we had to go out and I forgot to check it when we got home. It would be fun to see my wife's face if she finds it today. I just hope she doesn't fix it for dinner!

[Racer Z]

Yum. Relay soup with stuffed coils and fried plug wires. What's for desert? Thickened hypoid?

[Montana71-F100]

I had the same problem. My horn didn't work for years and I finally got around to fixing it. I changed the little metal box near the battery on the fender. I can't remember what it's called maybe it's the relay. The horn started working but at night I was awakened by my horn. It turned out to be in the pad on the steering wheel. The plastic that holds the rubber and flat copper was broken in a few places and the flat copper pieces that are supposed to touch when you blow the horn were too close. When it was warm there was no problem but when it cooled at night I got a rude awakening. Its been a couple of years but I think I fixed it with some epoxy like JB Weld or Waterweld, which is made by JB Weld. It's great stuff.