I had same problem. Bought a used distributor from a boneyard and it fired right up.
Check for fuel and spark - noting the age of the vehicle it may be the timing chain has "jumped"
If your Mercury Grand Marquis is a 1991 model or older . The 5.0 liter / 302 and the 5.8 liter / 351 has the distributor at the front of the engine The distributor rotor turns COUNTERCLOCKWISE
As far as I know , the 1991 Mercury Grand Marquis either had the 5.0 litre / 302 cubic inch V8 or the 5.8 litre / 351 cubic inch V8 engine . The 4.6 litre Single Over Head Cam ( SOHC ) engine was used in the Mercury Grand Marquis starting with the 1992 model year Firing order of the 5.0L which is the engine installed in the 1991 Mercury Grand Marquis is 1-5-4-2-6-3-7-8 rotor turns counterclockwise.
What year? check the ignition module. see manual
Check for a vacuum leak either under the hood or under the dash area
For a 1972 Mercury Marquis , 429 V8 engine : The firing order is ( 1 - 5 - 4 - 2 - 6 - 3 - 7 - 8 ) The distributor rotor turns COUNTERCLOCKWISE ( looking from the top ) The marked # 1 position on the distributor cap faces towards the REAR The engine cylinder locations are numbered : firewall 4 - 8 3 - 7 2 - 6 1 - 5 front of vehicle
Sounds like a Bad Sway bar link or possibly a strut/shock loose or bad
mercury
Mercury
it is the break light switch attached to the arm on the break pedal one of the wires broke or came off. the switch turns on the break lights and deactivates the lock keeping the transmission in park.
Mercury turns to a liquid at 25 degrees Celsius.
Mercury