My husband and Ijust bought a 2001 Mercury Grand Marquis. We both spent a sleepless night because we couldn't figure out how to get a tiny flashing light to go off on the headlight sensor located on the dash of the car. When I called the dealer this morning, they informed me that it is a security light and is supposed to blink continously 24 hrs a day if the car isn't in use. Is this true? Can it run the battery down? Can we turn it off? The operator's manual was of no help in figuring out what the blinking red light is.

Yep suppose to...
battery?? let see. the light is a LED or light emitting diode. in short no [img]smileys/smiley17.gif[/img]

A diode will forward basis at voltage treshold of .7V, and can flow a little current up to big time amperage. Most LEDs have a resistor set that will flow just enough current to allow the .7V over LED causing it to light up with 12V over the entire curcuit.
useing E=IR or R=E/I no.no.no.no I=E/R
let say the ckt is 100K ohm (R)
the ckt is 12V (E)
thats 120uA or .00012A, must car lights use about 1.2A and take quit a few hour to kill a battery and your starter uses up to and over 100Amp [img]smileys/smiley11.gif[/img]

or in english, yes it is supposed to be on constantly when you arm the the system. if you don.t like it on all night just leave the doors unlocked.

haha...i would rather have the light on then have people getting into my car!

maybe they have a garage Patrick. don't fret renebene, almost all newer cars have a small dash light or a flashing l.e.d. to let would be theives that your car has an alarm. it's just a theft deterrent it should'nt cause you and your husband sleepless nights. you want that little light to flash, unless of course,your car is a secure place.

Not Locking Doors Light Still Flashes. Yes, I have a 1999 that is in the garage every night. My wife hates the little flashing red light on the dash, but we know of no way to turn it off. We also travel a lot and may go off and leave the car for a month or two with its little flasher running down the battery with its very low current drain. We almost never lock the car doors, never have, we don't need an alarm and don't want to ever turn it on.[img]smileys/smiley2.gif[/img]