going in from the trunk where is the fuel pump located on 2000 grand marquis

It's in the gas tank, the tank must be lowered, not in trunk

Fuel cut off switch is (inerthia) in trunk by left rear trunk lid hinge.

Are trying to cut a hole in the trunk to get access to the fuel pump so you don't have to drop the tank if you are

I never done it that way I WOULDN'T RECOMMEND that method very dangerous!!!!

Just drop the tank it's not that hard.

Fuel pump can be accessed (albeit a tight squeeze) from front side (pushing exhaust to side) , no need to drop tank or cut hole. GHowever I am considering cutting such a hole to access fuel talk pressure sensor (to voltage test and possibly replace).