you dont
The stock amp in a 1990 Mercury Grand Marquis is in the dash behind the radio.
No
counterclockwise
8 spark plugs
Fuse or relay defective.
YES , a 1990 Mercury Grand Marquis 5.0 liter V8 engine has a PCV valve ( Motorcraft part number EV-98-B ) going into the intake manifold
Is the big silver plate on top of the engine that reads 5.0.
Check the engine end of the upper radiator hose
the fuel pump is located inside of the gas tank.
For a 1990 Mercury Grand Marquis : According to my Chilton's Auto Repair Manual : ( 20.0 U.S. gallons with the 5.8 liter / 351 cubic inch V8 ) ( 18.0 U.S. gallons with the 5.0 liter / 302 cubic inch V8 )
underside of the car in front of the fuel tank.
There is no fuse for the odometer. If it is mechanical and not working it most likely had a stripped or broken gear.