If the leak is in a brake hose, the cost would be about 25 dollars. If the leak is in a metal brake line, the best solution would be to get one from a junkyard. Do not put this repair off! The leak is going to get worse, and you will have no brakes!
If a rubber hose has a leak in it, replace it. Replace its opposite side companion at the same time. Costs will be from 25 to 40 bucks each plus fluid and time if you do it yourself. If you have ABS brakes and have run the system out of fluid, you HAVE to take the car to a mechanic that can work on ABS systems to have the system bled properly.
If you suspect that a metal line is to blame, the most likely place is going to be behind the fuel filter, just ahead of the driver's side rear wheel. This is a 3/16" line, and it CAN be patched with compression fittings, but I wouldn't recommend it. As for the cost? I really don't know, but if one of the rear metal lines is leaking, chances are the other is not far behind. Also, there are fuel return lines that run along with the rear metal brake lines. If you have a leak in the metal brake lines, your fuel lines are probably close also.
Replacing all of those lines can get quite expensive. Good luck.
with tools
DOT 3
According to the 1996 Mercury Grand Marquis Owner Guide : ( DOT 3 brake fluid , meeting Ford specification ESA-M6C25-A )
Check the brake light switch ,on the brake pedal. Might need adjusting.
Could be the tires, or your front brake rotors
Why ? Just replace it.
I have a 1996 Grand Marquis. If one of the brake lights goes out the signal on that side flashes faster. I would check the brake/tail lamps.
According to the 2001 Mercury Grand Marquis owners manual the fuse panel is below and to the left of the steering wheel , by the brake pedal , and has a cover on it
The brake light switch is bad. It's under the dash, and is switched by the movement of the brake pedal.
( # 16 ) is a 20 amp fuse for the cigarette lighter and OBD II in a 2007 Mercury Grand Marquis ( in the fuse panel below and to the left of the steering wheel by the brake pedal )
check your brake lights if they not worhing replace fuse or brake light switch
It could be a fuse. If the brake lights do not turn on when you press the brake pedal check your fuses under your dash.