DIY, change the tail light assembly on your Mercury Grand Marquis, the model produced in the years 1998, 1999, 2000, 2001 and 2002. This replacement will require an 11 mm wrench or a socket and probably a flat blade screwdriver. The process is simple and you can do it in less than half an hour.
To service the tail light on this car, you will have to start in the trunk. First, remove the plastic panel seen in the picture below. It has pins that hold it. You can just grab it by hand and pull it firmly, or you can use a flat blade screwdriver to remove those pins, if you find it easier.
After you do it, go behind the tail light and remove another retainer, a plastic knob like the one in the image below, that can be twisted counterclockwise. It holds the insulation in the trunk.
Once you move away the insulation, you will gain access behind the assembly and will be able to remove the three nuts that secure it and disconnect the harness that powers the light bulbs (see pictures below).
In the end, pull out the assembly from the body of the car, squeeze the rubber grommet on the electrical cable and remove the tail light completely. Move the light bulbs to the new assembly, or install a new, complete one, reversing the steps above. These are the simple steps you need to follow, if you wish to remove and replace the tail light assembly on your Mercury Grand Marquis, the model produced between 1998 and 2002.