DIY, change the side marker light assembly on your Mercury Grand Marquis, the model from the years 1998, 1999, 2000, 2001 and 2002. The replacement is quite simple and it will require a Phillips screwdriver, an 11 mm socket wrench and probably less than 20 minutes of your time.
You can start the repair after you open the hood of your car. You will have to remove the plastic cover above the headlights first. You can do that by twisting counterclockwise the pins that hold it at the extremities. They should look like the one seen in the image below.
After you remove the two pins and pull up the cover, go to the side marker light assembly, to the interior and remove the 11 mm nut seen in the image below. Use a socket with a ratchet and an extension to do it.
Now go outside the assembly and remove the Phillips screw located as you can see in the next picture. You can do it very simply, using an appropriate screwdriver. After that, pull out the assembly and twist the sockets of the light bulbs behind it, counterclockwise.
By doing that, you will be able to remove the old assembly completely and install a new one. You can reinstall it by reversing the steps shown above. This is all you have to do, if you need to remove and replace the side marker light assembly on your Mercury Grand Marquis, made between the years 1998 and 2002.