My 2003 Mercury Mountaineer alarm system goes off by itself sometimes. Keeps repeating even though I remotely cut it off. Last night I had to finally go out and start the vehicle to make it quit.

SOURCE: Alarm keeps going off at night

I don't know the exact reason, but my dad had a problem similar to yours. He got a device from Ace Hardware (it was a decoding mechanism I believe) that you hook up to your car (on his car, which was an Oldsmobile, it was on the left interior of the driver's side door rite up by the steering wheel area) for only about $15-$20 because his engine light was always going off for no reason. Yours may have something to do with a faulty wire somewhere along where the alarm is, though. The decoder doesn't exactly let you know precisely what the problem is though (I believe it has a manual though), and my dad is a mechanic, so be careful before you try anything yourself, as you may do more harm than good. Good luck.

SOURCE: how can I stop my 1997 mercury mountaineer factory alarm from

Set the alarm and sit still in the veicle. Just before the alarm goes off i would expect the door ajar light to come on with the alarm. It sounds like a faulty switch making the car think somebody is breaking in.

SOURCE: How do i check my charging system for my 2003

1st check the belt to the alternator. it should be in good condition and free of cracks. twist the belt so you can see the underside to check. if the charge light is on, this is a pretty good indicator that you have a bad alternator. if not get a cheep voltmeter and simply set to d.c. volts and put the leads on the battery terminals. voltage should be over 13.5 but not over 16

SOURCE: 2003 Mercury Sable alarm system goes on while parked

You may have a weak battery.

SOURCE: cabin filter location mercury mountaineer

There is one for the 2003 Mercury Mountaineer. If you are smellign a "vinegar" odor, mix a solution of 1 part bleach to 3 parts water and pour it down the grid at the base of the windshield. It will take care of the smell.