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Hey guys. Ford tech here. Been at this 35 years, so take it for what it's worth. There is a bladder type "switch" I. The air bag on this era Ford truck. It tends to collapse over time and when the temperature drops at night, it makes contact by itself, eventually always making contact and the hot will sound all the time. It is NOT the clock spring. When the clock spring breaks, the horn simply won't work at all. The easy diag is an ohmmeter across the horn contact connector after removing the air bag. If there's continuity, the only fix is an air bag replacement, or wire a different, maybe foot activated(?), switch to the horn relay coil wire then to ground. The horn relay is built into the central junction box, (relay panel). But there is easier access to that wire under the steering column where it leads to the clock spring.
fordmd, I have a theory on this, please tell me if this is possible.
I've got a '98 F150 that has started doing this. Researched the heck out of it.
I took my airbag off (battery disconnect, waited 20 min), and took the 2 torx screws off so I could pull the rubber horn pad down to expose the horn pressure pad. I checked it with a Ohm meter, and tested it - the pressure pad appears to be ok.
The pressure pad (copper pad) is sandwiched between the rubber horn pad (the part you hit), and another rubber pad that sits in front of the compressed airbag. On that inner rubber pad, i noticed some white powder (I'm assuming this is some sort of powdered lubricant, hex boron nitride or graphite), and the purpose is to provide lubrication between this rubber pad and the pressure switch.
My theory is that the factors of age, temperature swings, and humidity, have caused that powdered lubricant to wear off, and that when the inside of the cab is humid and heating up, with the rubber expanding at a different rate than the pressure switch, something gets hung up between the pressure switch and the rubber pad(s), things get 'stuck', and the horn goes off.
I'm going to buy some white graphite powder from the auto parts store, put some on the rubber surfaces that touch the pressure switch, then put it all back together and see if it fixes the problem.
It is my understanding that the powder is simply talc. At least it used to be, I'm not a chemist and haven't read that anything had changed. They typically tell us what we may be handling when there is a change in build method. Anyway, the reason for the powder is to lubricate the air bag as it deploys, but very well could have had a benefit for the horn pad. In my experience, the horn sounding on its own occurs at night when it's most inconvenient and colder, therefore change in dimensions could be occurring and you're theory holds up. Honestly, I hadn't been pushed to think that far into it, thanks for the push.
Originally Posted by jackrterrier
fordmd, I have a theory on this, please tell me if this is possible.
I've got a '98 F150 that has started doing this. Researched the heck out of it.
I took my airbag off (battery disconnect, waited 20 min), and took the 2 torx screws off so I could pull the rubber horn pad down to expose the horn pressure pad. I checked it with a Ohm meter, and tested it - the pressure pad appears to be ok.
The pressure pad (copper pad) is sandwiched between the rubber horn pad (the part you hit), and another rubber pad that sits in front of the compressed airbag. On that inner rubber pad, i noticed some white powder (I'm assuming this is some sort of powdered lubricant, hex boron nitride or graphite), and the purpose is to provide lubrication between this rubber pad and the pressure switch.
My theory is that the factors of age, temperature swings, and humidity, have caused that powdered lubricant to wear off, and that when the inside of the cab is humid and heating up, with the rubber expanding at a different rate than the pressure switch, something gets hung up between the pressure switch and the rubber pad(s), things get 'stuck', and the horn goes off.
I'm going to buy some white graphite powder from the auto parts store, put some on the rubber surfaces that touch the pressure switch, then put it all back together and see if it fixes the problem.
The switch in my 2006 is a sealed unit that can be removed the same way.
You can even buy the switch from Ford. But it's not cheap. It's almost the
same price of a new airbag.
Have a look at the 2006 switch.
With the screws out the switch comes right out and there is no talc on the airbag.
The switch is heat sealed on the edges with no way to get into it.
Yahiko, thanks for the pictures, my 1998 version looks the same, same pressure switch manufacturer too.
Fordmd's explanation for the talc/powder makes more sense.
The three instances where my horn went off, one I was driving (I was able to get it to stop by hitting it), another time sitting in the driveway (again hit it), and the last time was again in the driveway (that time I had to yank the battery cable).
I did notice the last time it happened, hitting the horn pad didn't stop it, but pushing up on the lower part of the horn pad would stop it temporarily.
I don't think my pressure switch is bad, and I don't think it's an electrical failure - seems to be mechanical in nature. By that, I mean that the pressure switch is being activated by the rubber horn pad (the part you hit), and it seems to be due to heat/humidity (I live in the southeast, yesterday it was in the 90's and humid).
I wonder if things like, not completely tightening the two torx screws (leaving some 'give' so the rubber horn pad can move), or sanding down the ribs on the inside of the rubber horn pad would help?
For 2006 the switch is available. Prior years as the 98 and 01/02 I've been responding to it isn't available seperately. It does give me an idea, however. All horn swiches are a simple two wire swich that grounds 12 volts coming from the horn relay coil.
Originally Posted by Yahiko
I think a true "OFF" switch would be a good idea with the train horn.
That way you g=don't get the midnight express wakeup call.
Maybe a push button and a relay? When the power is off, relay grounds, keeps horn from blowing. turn engine on, relay opens, power to the horn. The push button is an override, to kill the horn if it starts sounding while driving. Button shorts the horn circuit when energized and pushed. So, you would have to turn off then back on the engine to reset the button, if you want your horn to work.
Maybe that over-complicates things, it would be nice if the horn just worked as it was designed. A simple on/off switch would be easier. That's probably the solution I will do. Only problem is forgetting the switch, or when someone borrows my truck and doesn't know about the switch.
pictures of my pressure switch. there are horizontal ridges, from the backside of the rubber horn pad (part you hit). Also mine has dimples on it whereas Yahiko's does not (mine '98, his newer).
I wonder if the rubber ridges on the backside of the rubber horn pad are getting hung up on the pressure switch in these ridge depressions, and as heat/humidity causes things to expand, it's actuating the pressure switch?
Yahiko,
Thanks for the write up with pictures. A fast & easy fix. I bought a used horn/air bag assembly that the pad wasn't in too good of shape but the switch ohm'd out good and just swapped out the contact pad from that one to mine. All is well.
I'm having an issue with my horn as well. 2001 F350 7.3. A couple of weeks ago, the horn started blowing about midnight. Scared the bejeebers outta me. Disconnected the battery and read about possible causes online, figured I'd deal with it later.
A few days later, with battery still disconnected, I dismounted the airbag and disconnected the horn from it's electrical connection thinking that the horn pad was bad. Left everything else intact.
Fast forward to today. Was out running some errands in another vehicle and I got a call on the phone that my truck horn was going sounding continuously. It was parked at my dad's house and wasn't locked. He seemed to have some success getting it to shut up by opening the front drivers side door but it would start sounding again shortly after. I disconnected the battery again.
One thing I did note this time, though, was that it rained yesterday, about 2", and it's interesting that today is the first day it's done that. It's been dry here for the previous several weeks other than the occasional shower that didn't amount to much. Yesterday, it pretty much rained all day long. Hmmm.
I'm thinking I'm gonna have to go looking around in the area of the fuse panel but don't know for sure just yet. I've heard that there can be leaks that can get in and do some damage to that area that can cause this issue. I have wondered, also, if I can get the thing to behave again, whether I can put some plastic in a strategic manner so that if such leaks occur again, that they won't be able to get to said fuse panel location. (??)
It's an old truck with almost 350k miles on it so it's not gonna get a nice cushy trip to the dealer for a makeover. It's sole purpose is to haul my rv and that's about all it gets used for. I do need it for a little while longer, though, and it sure would be nice to have a horn.
Figured I'd chime in since I'm obviously not the only one.
I did have the windshield replace a couple of years ago but I'm not sure that's where it's leaking in. (?) I saw the guy schmutzin' up that new windshield and he certainly did use enough schmutz.
Anyway, I'll let you all know what I find. Might be that drying out that fuse panel might be the ticket, like someone said before, but we'll see.
I'm having this issue with my 2002 Excursion. The horn turns on when it is sitting in the sun warming up. Tapping the horn lightly makes it stop, for a little while. I'm going to try a Dorman replacement switch.
Horn blows continuously after I lock doors with remote
fordmd
i ran across this old thread while doing some research. I have a 2006 F350 that occasionally when I lock the doors with the remote, the horn begins to sound continuously until I remove the fuse. It has happened to me twice and both times, a few days later, I put the fuse back in and everything is fine. It never seems to stick when I push in the horn. I thought it was probably the horn relay sticking closed because the horn chirps when you push the lock button twice. I am gathering from some of these conversations, that the horn relay isn’t easily replaced. It doesn’t seem like the same issue that others are having that you have identified as a bad horn switch/air bag problem. Any ideas?
thanks
George
Originally Posted by fordmd
Hey guys. Ford tech here. Been at this 35 years, so take it for what it's worth. There is a bladder type "switch" I. The air bag on this era Ford truck. It tends to collapse over time and when the temperature drops at night, it makes contact by itself, eventually always making contact and the hot will sound all the time. It is NOT the clock spring. When the clock spring breaks, the horn simply won't work at all. The easy diag is an ohmmeter across the horn contact connector after removing the air bag. If there's continuity, the only fix is an air bag replacement, or wire a different, maybe foot activated(?), switch to the horn relay coil wire then to ground. The horn relay is built into the central junction box, (relay panel). But there is easier access to that wire under the steering column where it leads to the clock spring.
I'm reviving this thread yet again... My horn has always been pretty hard to push. I took out the horn pad a few months ago to see if I could find anything binding up, but turns out it was just wearing out.
About two months ago my horn started blasting on a cold evening, and my girlfriend's dad's truck was going off as well. I thought he was messing with me, because as soon as I hit my panic button everything stopped. In a drive-through, my horn started blasting for about ten seconds. It then did it again, and I had to dig up the owners manual to find the horn relay. I thought it was a stuck relay, I removed the relay and broke the case open and saw a lot of corrosion, so I put the driver window relay in place of the horn relay. Sure enough, at midnight, my horn blasted and I had to pull the relay again.
A Dorman (whom I avoid like gas station hot dogs) unit is around $100-120. I pulled a horn pad from a 2000 Super Duty in a junkyard for $22 and it looked like it was in perfect condition. I just put it in today. The horn is WAYYYYYY easier to push.
I tried to repair my horn like this thread: https://www.powerstroke.org/threads/...airbag.125167/
My horn pad looks slightly different than the one in that thread, and I noticed that most horn pads say they work on 02+ trucks. I kinked the copper and then gave up, I figured I would get one from the junkyard or just buy the Dorman one if I couldn't find it. I got lucky, but maybe you guys will have similar luck finding a horn pad at a junkyard.
Happy New Year 2016 is almost here 
