Do it yourself, change the headlight assembly on your Mercury Grand Marquis, the model produced between the years 1998 and 2002. The replacement process is quite simple. You will not require tools, just a new headlight and probably less than 20 minutes.
You can start above the headlights, by removing two clips that hold a plastic cover, as you can see in the images below. You can do it by hand, by twisting them counterclockwise and pulling them out afterwards. After you remove that cover, you will be able to work on the headlights.
Now, in order to service them, you will have to pull up and out the two metal tabs seen in the picture below, that secure them onto the body of the car. You should be able to do it by hand, but if you find it really difficult, you can use a pair of pliers or some other tool.
After you release those tabs, pull out the assembly and disconnect the two harnesses behind it, that power up the light bulbs. Now the bulbs can be replaced or moved to the new assembly, if needed. If not, move on to install the replacement headlight.
Make preliminary adjustments to the new assembly before installing it, then reconnect the harnesses behind and secure it inside the front bumper with the metal tabs. In the end, place back the cover above the headlights and that’s it. This is all you need to do, if you plan to service the headlights on your Mercury Grand Marquis, the model manufactured between the years 1998 and 2002.