At the front of the engine , towards the drivers side of the engine ( power steering fluid reservoir on a 1998 Mercury Grand Marquis )
It is part of the power steering pump assembly.
I was looking at a picture in the 2003 Mercury Grand Marquis Owner Guide and it shows the power steering fluid reservoir at the front of the engine compartment between the engine coolant reservoir and the engine air filter box
My 1997 Grand Marque steering is binding when making a turn. Power Steering Fluid is FULLL.and system isn;t leaking.
Directly behind the steering wheel.
DOT 3
It is on the back of the power steering pump. The power steering pump is located on the left hand side of the engine. It will be a cap with the dipstick molded on to it. Remove the cap and you will be able to see the fluid.
Your 1996 Mercury Grand Marquis may need a new transmission or something as simple as transmission fluid.
According to the 1996 Mercury Grand Marquis Owner Guide : ( DOT 3 brake fluid , meeting Ford specification ESA-M6C25-A )
the fuse box on a 1991 ford grand marquis is located right under the steering wheel
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
fuse box under steering wheel