One problem related to alternator/generator/regulator has been reported for the 1996 Mercury Grand Marquis. The most recently reported issues are listed below.
The car started normal at work and drove 20 minutes to home. Placed car in park, and attempted to turn ignition to off, but the key switch rotated freely with no resistance. The key switch was tried again to turn off ignition by turning in either direction fully with no affect. Key was removed, switch rotated freely. Steering could not be locked. Then attempted to stop engine by another method. Lifted hood and disconnected battery - alternator keep it running. Owner manual showed ignition fuse which was pulled to stop motor. Switch was still in on position when battery was reconnected. The car could not be restarted by key switch. Battery disconnected to disable airbag until repairs could be accomplished. Repairs: I did this myself. The steering column had to come completely off. I determined it would take 5 to 6 hours of work to identify problem and fix. A dealer would have charge for this. After steering column was removed the switch mechanism was examined for problem. This was a tilt type column. A plastic shaft extended from the key switch across the tilt area to a plastic switch actuator in the main column shaft. A thin 1 inch long steel bearing type pin was found stuck to some grease. The column was taken apart and it was determined the pin fit into a hole in the switch actuator. This pin was forced back into the hole, super glued, and steering column was reassembled and placed back in the car. Loose shifter bolt tightened. Ignition switch was checked. Slider had resistance to being moved and showed some contact burns. The ignition switch was replaced. Steering column with fixed switch actuator was installed. Car started normal with no resistance to ignition. Turns on and off normal. Consequence of ignition actuator link failure is high danger with a stuck accelerator or parking in a confined space (garage). Engine can not be turned off in dangerous these situations or an auto accident. Switch actuator is poor designed with parts that fall out.