Keep in mind if this is an aftermarket alarm system the dealer is going to tell you to take it back to the people who sold you the alarm, not to mentions the cost to have a dealer work on it if they decide to help you. Ouch! This is NOT a difficult problem to troubleshoot. You can do it with a schematic and a DVOM. I'd be willing to atempt it without the aid of a schematic as long as I could locate the horn relay which isn't hard to do. If your alarm is putting ground on the control side of the horn relay the horn will sound. If you look at the underside of the horn relay socket you'll probably see a wire coming from your alarm soldered to the horn relay control side ground wire. Disable the alarm(pull fuse) to see if the horn stops. If it does you know the alarm is the problem. If not you have to see if the horn switch is shorted. Ford puts the horn switch inside of the airbag on some models. The horn switch can either go short or go open. You can't fix it either way if it is inside of the air bad. You have to remove the airbag(kill power) to get to the wires going to the horn switch which are located behind the airbag. You cut the wires going to the switch and solder on some leads. You drill a hole in the top of the steering column. You pass the leads you soldered onto the horn switch wires through the hole you just drilled Then attach a doorbell switch($5 at your local hardware) to the leads. Done! Either that or you can pay $800.00 for a new airbag which just happens to come equipped with a new horn switch. The choice is yours. I know which way I do this repair. Parts $5 Labor 1 hour.

 

This is not an aftermarket alarm system it is the Ford dealer alarm that came with my 2006 F250 Diesel Lariat FX4. By the way, I am a second owner and I think that was the reason it was sold since the truck it is in more than excellent conditions with 65000+ miles when I bought it. I tracked the ownership of it and was bought at first for a building company. I am really happy with this truck but the alarm is driving me crazy .

I cannot turn on the truck when the alarm started. It is a constant sound and not an intermittent one, but only happens when temps drop. It will even sound if I connect one battery (either left or right) and the temps are still under 46 for example.

I "know" ($$$) the consequences to take it to a dealer, but I already took it to another place and they suggested me to address it to them.

Sorry, I am not too proficient with mechanical specially electrical ones , and I just came up for an answer that I think I found. The Mustang sounds pretty much familiar adding the temps of course, and apparently I am not the only one with this kind of issue.

Thanks eallanboggs.

 

OK! it was the horn and cost $$700+++. No problem so far with temps under 40 and still under observation, but I feel it is done. No wonder I couldn't do anything but take to the dealer. Now, I like more my truck!

 

$700 ? Ouch, I think I would have just rolled down the window and yell HONK for that much.

 

I would have fixed that for under $100 including parts($5 doorbell button at ACE hardware). I've made this repair many times(mostly on Lincoln Town Cars) and the owner is happy when they find out they don't have to pay for a replacement air bag($600 plus at dealer) to fix their horn. Some people say they don't car if they have to use a doorbell switch to blow their horn since they only blow it one time a year during the annual vehicle inspection.

 

I put a new battery in my trunk f-150 and the horn keeps going off if you open the door.we took outthe fuse for the horn and now the flashers blink .please help the guy who put the new one in took some thing off and said it was a add on alarm but it is off .please help me if you can't be nice don't say anything.

 

I once took my shoes off and my jacket unzipped itself. I'm still trying to figure that one out. Maybe it was too much Cabo Wabo?
Factory alarm; go to dealer
Aftermarket alarm: go to alarm store
or disable the alarm

 

Why so rude ?

 

$700 to replace the horn... the thing under the hood that a loud sound comes out of?

 

Probably the flashers were also blinking when the horn was blowing but you just didn't notice. These are both functions commonly controlled by an alarm system.
My guess would be that something needs to be reinitialized on the alarm system. It probably has some type of internal battery that will keep it in a powered state even if someone messes with the vehicle power (like disconnecting the battery).
I suggest you find the model # of the alarm and search on line for a manual if you don't already have one. It will likely give you some info on resetting the system, or take it to an installer, they probably know what to do without even looking it up.

 

[qote=weslhg;9696330]We have the same problem. Have you found a fix, if so can you please post it.[/quote]
Had the same problem with another car a few years ago. A neighbor suggested we change the steering wheel cover for the horn. Amazingly, that took care of the problem. Seems the vinyl would contract in cold weather, creating the problem.
Just saw this post-----two months after the original post---sorry.

 

See if the solution is in this post:
https://www.ford-trucks.com/forums/1...reset-fyi.html

For Ford System 3/4 Alarms.
Disconnect the battery. Wait 2 minutes for the module to lose all traces of voltage. Turn the ignition key to the RUN position. Reconnect the battery. Shut the key OFF and press LOCK on the drivers door switch. It's called reinitializing the alarm.