Probably need to replace the brake light switch, under the dash. check to see if you are under warranty. it is very important to get all problems solved before your warranty gets up.
Remove the wing nuts from inside the trunk. Just pull the housing out after.
with tools
Mercury Grand Marquis for one and I am sure there are others that I am not familiar with
Could be the caliper or the metal line. You will have to have it checked.
blown fuse or turn switch bad
yes
Not that I know of , just rear wheel drive on a Mercury Grand Marquis from the factory
What fuse is for the 2005 Ford mustang Rear Brake lights?
On a 2001 Mercury Grand Marquis : The fuel tank is mounted vertically behind the rear seat
on a 1997 Mercury Grand Marquis kill switch be activated by a rear end collision
the turn signal switch is probably bad
it would be the brake light switch about 20 dollars at autozone