Disable factory alarm

If your talking about the horn, fuse 28--20 amp underhood fuse box. That is just for the horn.

There isn't one the alarm if factory fitted is integrated into the ecm so to disable the alarm you would need to disable the engine control module

You may be able to disable the alarm, by opening the door with the key. Or pull the fuse, to the alarm system in the fuse box. Open your key fob remote, and check the internal 3v battery as well. It could be dead, or the (outer) case buttons are not making contact with the board which has the actual buttons on it. When pressing the buttons manually on the board they should make a "click", else wise they are the source of your problem in the remote.

If it's a cheap aftermarket alarm, check for a red wire coming off the hot side of your battery with an inline fuse. If it's not, try to locate the alarm "computer" under the driver's side dash or nearby your fuse panel. You'll find a black box with a wiring diagram glued to the side, normally strapped to a wiring harness or other fixed element. If this is the type of alarm you have, you'll need to trace each wire coming from the alarm computer and unclip each fastener that's clipped to your vehicle's factory wiring. The trouble with these types of alarms is that they can get power from a number of sources (stereo, interior lights, etc.). Good luck with this one!

Do you know if the alarm was factory installed on the vehicle? If it is then look in the fuse box and there should be a diagram showing which fuse is for what and then you can take out the fuse that says alarm.

Find the alarm's fuse. It may be in the fuse box, usually located below the steering wheel to the left. Many cars also have other fuse boxes (sometimes three or even more) inside the engine compartment. If it's an aftermarket alarm (installed after the car left the factory), you'll find the fuse under the hood, usually on a wire connected to the positive battery terminal.

Locate the fuse that has the alarm label. You should find a fuse diagram on the lid of the fuse box. An aftermarket alarm won't have any label. Don't worry; removing the wrong fuse won't cause any damage. If you pull out a fuse and the alarm stays on, put that fuse back in and try another.

Pull the alarm fuse with the fuse puller (sometimes found in the fuse box) or a pair of needle-nose pliers. Sometimes you can remove a fuse using your fingers.

there is one under the hood and one on the drivers side end of the dash in between the door and the dash. If its the factory alarm you will not be able to disable it by pulling a fuse. If its an aftermarket alarm its fuses will not be in the fuse boxes.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

factory alarms have fuses too. try looking in the fuse box... remove the fuse and it'll disable the alarm...

I had this problem with an aftermarket alarm on my accent once.  Check your battery cables and terminals, if there is a bad connection or any corrosion this will cause the alarm to act up.  if that is not the problem, try the fuse box, see if there is a fuse labeled alarm or something like that, if nothing else important is on the same fuse just pull it out.  Or you could just locate the horn for the alarm and cut and cap the wires on it.  That would disable the alarm from making any sound, all other functions would remain intact.  good luck.

what year is the Mustang? It does sound like the factory keyless entry module and the clicking is a relay inside of it. In order to disable the clicking, you would need the factory keyless entry remote or the aftermarket alarm system would have to be correctly wired to the vehicle's alarm disarm wire. A professional stereo shop would be able to handle this for you.