The spark pluggs are in the engine you got to take off the air intake manifold sounds crazy but if you know about cars you kno its not if you don't know what I'm talkin about you should probably leave the job to some one who does good luck
How Do I Change The Spark Plugs On A 99 Grand Marquis?
Where Are The Spark Plugs On 1999 Mercury Grand Marquis? I am trying to change the spark plugs. How do I get down to where they are?
Extensions and universal joints! And you should hope that you have the fully threaded ones in there. Do not use the plugs that are only partially threaded since the allow debris to accumulate in the threads above and can make them next to impossible to get back out! Trust me when I say I learned this first hand!