* Sockets and wrenches: A variety of sizes, likely both metric and standard, will be needed to disconnect the electrical connectors, air lines, and mounting bolts. Expect to need at least a socket set and a wrench set.
* Ratchet: A ratchet will significantly speed up the process of removing bolts.
* Extensions and possibly universal joints: To reach those hard-to-get-to bolts.
* Screwdrivers: Both Phillips and flathead, for removing any plastic covers or access panels.
* Jack and jack stands (and wheel chocks): To safely lift and support the vehicle.
* Wrench or socket for the air line connections: These may vary greatly, but often require a specific fitting.
* Possibly a torque wrench: For tightening bolts back to the manufacturer's specifications after reinstallation.
Before starting any work, consult a repair manual specific to your 1998 Mercury Sable. This will provide diagrams, torque specifications, and step-by-step instructions. Improper removal can lead to damage to your vehicle. If you're not comfortable with automotive repair, it's best to take it to a qualified mechanic.