The Mercury Grand Marquis was manufactured with electric windows, each of which uses a motor to drive the window regulator. The motor can wear out and require replacement, which involves removing the door panel and some molding. The procedure, for any door on the car, will take the average backyard mechanic about 30 minutes to complete.
Disconnect the battery at the positive terminal. On the Grand Marquis, this is a post style battery with a bolt and nut. Turn the nut counterclockwise to loosen the terminal, and place it away from the battery.
Remove the switch assembly. Pry up the corner of the assembly molding with a screwdriver, then carefully tug the switches out by hand. Pull apart the adapter plug that connects the switches to the wiring harness. Set aside the switch assembly.
Take off the door panel by removing all screws, bolts and pop rivets that hold it in place. The screws in the interior door panel and the bolts in the armrest can be removed by turning them counterclockwise. The pop rivets, which hold the door panel to the metal, are feathered plastic bolts that grip their holes in the metal. Pull the door panel firmly from one corner, and the rivets will begin to come up. Continue to pull around the panel and disengage rivets until the panel is freed. Be ready to replace several of the pop rivets, because they are usually brittle after years of service. Place the panel away from the work area.
Remove the motor by turning the two or three mount bolts counterclockwise. The number of mount bolts depends on the model. Disconnect the motor from the wiring harness by pulling the adapter plug apart. Pull the motor away from the regulator gears, and replace it with a new unit. Inspect all window regulator hinges and lubricate them if necessary.
Position the new motor into the regulator gears and tighten the mount bolts. Reconnect the wiring harness, and replace the door panel by tapping the pop rivets individually. Replace the armrest bolts and door screws by turning them clockwise, and reconnect and replace the window switches by pressing them back into the Marquis' door panel opening. Test the window.
