You can't disconnect the 4-wheel drive. The Mountaineer is a ALL WHEEL DRIVE S.U.V.
Replace the transfer case , had same problem and that's what it was.
On a 2005 Mercury Mountaineer : All Wheel Drive ( AWD ) has engine power going to all 4 wheels , all the time , and doesn't require any driver input
( 4R70W ) automatic transmission is used on the 1998 Mercury Mountaineer 5.0 L - V8 all wheel drive
The fuel pump is in the fuel tank.
Bank 2 is the drivers side of the engine in a Mercury Mountaineer Sensor 2 is in the exhaust after the catalytic converter ( downstream )
There isn't one. In 1997, mountaineers were either 2 wheel drive or all wheel drive. Not 4 wheel drive
According to the 1997 Mercury Mountaineer owners manual : ( 13.9 quarts / 13.2 liters ) for the 4R70W automatic transmission ( rear wheel drive and all wheel drive ) ** that would be for the entire system , transmission , converter , lines , etcetera **
If your vehicle has 4 wheel drive, then yes, it has a differential in the front axle.
Look under the the plastic cover on the drive side by the breaks and gas pedals
The check " gage " light on in your 1997 Mercury Mountaineer indicates that either your engine oil pressure is LOW , your engine temperature is HIGH or your gas tank is AT OR NEAR EMPTY .