The good folks at Chilton say no you remove the plenum from under the dash and then remove the heater core from the plenum. You may want to get the book for this one as they're are about twenty steps (many things to remove) before the plenum will come out. Good luck.
no
Major operation. If you still wanna do it yourself, get a manual, like a Chilton, and follow it exactly.
I couldn't find one in the fuse layout page of the manual that came with my 1987 Grand Marquis. I would assume not.
Inside the Gas Tank. You must purge the Gas Tank, lower it, replace the filter, then reassemble.
18 MPG.
The factory radio on a 1987 Mercury Grand Marquis is made to play local radio states and cassette tapes. It is connected to a high fidelity sound system.
Clarify....Are you talking about an AMP for a Stereo?
According to my Chilton's Auto Repair manual : A ( 1987 ) Mercury Grand Marquis has a ( 20 U.S. gallon gas tank )
autozone.com
NO a grill from a 87 will not fit a 91. Only a grill from 88 , 89 or a 90 will fit. They don't even look the same.
under the dash, driver side floor
At the St. Thomas Assembly Plant (STAP) in Ontario, Canada