Try Pulling the handle you open the door with. Sometimes the latch gets closed while the door is open and it feels like it's hitting something solid and won't close.
in the trunk on d/s is a bypass door opening cable if the incar cab lever wont work
grand marquis
usually the locking latch in the door is in the closed position. try holding the handle in the open position and opening the latch manually.
Probably a bad starter solenoid.
Check the ignition coil on the Marquis. Check the crank sensor as well. One of these is probably bad.
Sounds like a bad Brake Light Switch. It's located on the steering column.
Mercury changed the style of the Grand Marquis in 1995. 92-94 are compatible, 95-97 are compatible. You might be able to force it and figure out a way to get it to work, but it probably wont look good. My family have a 1993 and 1997 Marquis, and the front ends are different.
The safety override switch is probably on. If not, then the motor or switch may be bad.
check your brake lights if they not worhing replace fuse or brake light switch
Access in rear door panel, allows you to lock/inlock rear door.
does the light illuminate during start up? If not the lamp is burned out. If it does, then the engine computer is likely at fault.
I'm not a mechanic / technician but it sounds like you have a dead cell in the battery ( or a bad battery cable connection ) Does anything else work on the vehicle after you shut it off , such as the headlights or if you have the drivers door open with the keys in the ignition do you hear the door chime