Was needing to know the fuse number for my fuel pump and
Where is the relay located, for a 2000 mercury sable ls

I believe it is fuse #16, which along with the fuel pump relay, are located in the under hood fuse/relay box (see underside of cover). With the fuel pump relay (small relay on the back row), try substituting another identical relay inside the fuse/relay box. If it solves the problem, buy a new relay.

If you don't hear the fuel pump run, when you turn the ignition switch to run, check all under hood and under dash fuses with a test light or multi-meter, plus reset the fuel pump's inertia switch in the trunk.

Should be in the owners manual and under the fuse and relay cover.