We suspect you do:

 

No, the only alarm we have is whatever 'alarm' came with the truck when it was new. It came with two keys, both with their own remote access lock/unlock key FOB. Press lock and all the locks went down, and if you tried to start it, even sitting inside, without first having hit unlock, then the alarm siren went off and the truck would not start - theft light blinking. Nothing else has been added. The alarm siren hasn't worked since the horn went out, which I think is a broken wire going from the under-hood fuse box over to the horn. I once had my son put 12 volts the horn and it worked. If I was able to, I go under the truck and find the broken wire & fix it,.

 

So, it does have a non-factory alarm installed, quite possibly a dealer-installed system as the factory did not include them. You'll have to dig under the dash above the pedals to see what,exactly is there.

It is likely your problem.

 

I learn something new every time I come here. I assumed because we got the 2 key fobs with the truck when new, that it was a factory alarm. However there is a flashing 'valet' light/button on the lower dash panel, below the steering wheel. I'm learning that 'valet button/light' may not be factory installed. So maybe that thing has been the problem all along. What I don't understand, (because I go through life clueless) is if the truck comes from the factory with the two unlock/lock key fob's, how and when do they incorporate the valet button into the system? Does the dealership do it? Or do they have someone come on the lot and do it? We've never used the valet button so I don't even know how the thing works. It wouldn't bother me to remove it but I don't want to make things worse.

 

So I had a 2003 Ford Escape that somehow didn't get ordered with a remote start and premium alarm system. So there was an option for the Ford Alarm System (aftermarket), but they still had to cut into wires and was not plug and play (didn't find that out either till AFTER it was installed!). Dealer offered it for free with free install.

Was not happy at the time, but it was too late and I signed for the vehicle.

IIRC, there was a valet button/light. It's been a while, but I remember having a different Ford key fob that controlled that system. So basically it had the factory unlock fobs that still worked, then the Ford aftermarket alarm key fob. However if you armed the aftermarket, and used the factory fob, it would enter the vehicle into alarm mode. It was a very strange "mickey mouse" setup.

You might actually have a system like that. Where it does actually have a crossable Motorcraft part number.

 

Several years ago, some dealers installed an aftermarket system on vehicles on their lot in an effort to reduce car theft off their lots. That was the case with one I bought in 2005.