Where is the fuel pump fuse in a 1998 mercury mountaineer?

The 1998 Mercury Mountaineer's fuel pump fuse isn't a single, easily identifiable fuse labeled "Fuel Pump." Instead, the fuel pump circuit is protected indirectly, often through a relay and potentially several fuses related to power distribution. You'll need to consult your owner's manual. It will have a diagram of the fuse box(es) and specify which fuse(s) are related to the fuel pump circuit.

Without the owner's manual, locating the correct fuse will involve a process of elimination using a multimeter to check for power at various points in the fuel pump circuit and testing fuses suspected to be in that circuit. This is not recommended unless you have experience with automotive electrical systems. Incorrectly diagnosing the problem could cause further damage.