What comes in common with the tech curses control and speedometer not working with a 2002 mercury sable

SOURCE: mercury sable 2002 serpentine belt change

There are also two serpentine belt types for the 2002 sable. The S and U type engine. Take the old belt with you the the parts store. As for the diagram, I googled it under images and about a dozen correct ones came up. Remember the 2002 sable is the same as the 2002 Tarus.

SOURCE: where is the fuel pump in 2002 Mercury Sable

it is in the gas tank you have to drop the tank and it goes down in the top although i would locate the filter on the frame rail first and replace it its cheaper and i reccomend you replace it anyway with a pump change

SOURCE: cruise control for 1994 mercury sable four door

There are numerous things that can cause this. A fuse, a vacuum leak, a bad switch in the steering column. The switch in the steering column is usually the culprit but is also the hardest and most expensive to change. Best way to find out is to plug it into a computer and see if it reveals any trouble codes.
Also of the many things that can go wrong outside of replacing the servo controller.
Check the servo deactivation switch. Located on the brake pedal arm under he dash. This will require you to remove the black plastic duct fot shield to expose the under dash area. It only has 4 plastic speed grommets. You will see to switches on this brake arm.
The lower one activates the brake lights. The upper one deactivates the cruise control and is a common failure in 1998-2002 Ford mercury Crown Vics and Marquis. Remove the connector(also known as connector c223), and check the continuity of the switch opened or closed. It should change from infinite to a short using a standard voltage meter set to ohms or continuity and pushing the brake pedal.
Also Fuse number 1 (15amp blue fuse) located there under the dash as well, is the primary fuse for the cruise control servo. In most cases you will see this ok

SOURCE: Remove the right rear door panel in a Mercury Sable

Removed two screws from the perimeter of the door, one in the back edge and the other under the bottom. Remove one screw from the handle cup where the window switch is located. Placed some tape around the edge of the handle cup for protection against scratches and pried the cup out with a small putty knife. It is hard, but will pop out. Next I taped the paint around the door panel and used a flat bar to reach behind the panel and had enough of a gap to see the orange tabs and pried each one to remove the panel completely. The panel does not need to be lifted up to removed, just pull it straight off the door. A few tabs may still be holding, but will pop off with a bit of pressure.

SOURCE: 2002 Taurus: how many ball joints on a 202 mercury sable...

there are 2, a lower ball joint on each side.