I recently purchased a 2004 mercury grand marquis. I have the factory key code. I need to know how to change it because someone know it and has been in my car

SOURCE: Factory Keyless Entry Code

mine was located on the right hinge in the trunk

SOURCE: Purchased a used 2006 Mercury Grand Marquis, did

Ok there are 2 ways to retrieve the key-less entry code. First and easiest way is to carry it to a shop that has a scan tool that can read pid data from the driver's door module .They can pull up that pid and display your code right on the screen.
The second and hardest method is to remove the driver's door panel to access the driver's door module and there will be a tag on it with the 5 digit code.
Yes you can program your own code into it however you must have the original code .Input the original code then hit the number 2 button then put in your own 5 digit code.This code will remain until you disconnect the battery or battery goes dead then it reverts back to the original.
You can also go to this website and download your owners manual for free. Just pick owner guide in the left task bar and input your vehicle information.

http://www.genuineservice.com/genuineservice/en/default?page=genuineService

SOURCE: Can someone post a fuse diagram for 1991 mercury grand marquis ?

they don't have diagram that i've seen, my roommate has this car and on page 172 of owners manual it gives the number of what fuse does what,, .. which corresponds to the number on the lid of your fuse panel

SOURCE: im trien to reset the factory car alarm and code

usually if you go to the dealer they wont charge you.Let them help!

SOURCE: 1994 Mercury Grand Marquis Check Engine Light Code 332

its the tube going from the egr valve to your exhaust it have carbon build up and you either have to replace it or get a metal coat hanger and clean it out.