You would add DOT-3 brake fluid to the master cylinder brake reservoir. If your not sure please stop by an auto parts store and ask for help. If you have to add brake fluid to the reservoir you need to have the brakes inspected for repair or replacement.
If you mean the exclamation point and the " P " above the word " BRAKE " in the lower right side of the gauge cluster in a 1998 Mercury Sable that means either the parking brake / emergency brake is on , or the brake fluid level in the brake master cylinder in your engine compartment is LOW
According to the 1998 Mercury Sable Owner Guide : ( Motorcraft MERCON automatic transmission fluid is used as the power steering fluid )
Motorcraft MERCON automatic transmission fluid is used as the power steering fluid ( according to the 1998 Mercury Sable Owner Guide )
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According to the 1998 Mercury Sable Owner Guide : ( Motorcraft MERCON-V automatic transmission fluid )
DOT 3 brake fluid
D O T ( 3 ) brake fluid
The brake lights on a 1998 Mercury Sable are changed by removing the retaining screws, pulling the light assembly away from the vehicle, and removing the bulb. A new bulb can then be installed and the assembly put back in place.
Front wheels off the ground (tow truck or dolly) parking brake off
On a 1998 Mercury Sable : The fuse box is under the drivers side of the dash , to the left of the brake pedal ( it has a cover on it ) Also , the Power Distribution Box ( which is " live " ) is located in the front of the engine compartment , near the battery
In a 1998 Mercury Sable : The transaxle is the transmission on your front wheel drive Mercury Sable it is located in the engine compartment , on the drivers side , bolted to the engine
According to the 1998 Mercury Sable Owner Guide : ( 16.0 U.S. gallons )