Either one of your rear air bags have a leak or both have went bad.
It is in the right front corner of the engine compartment (passenger side)
On a 1998 Lincoln Navigator I believe it is in the front passenger footwell ( it might be behind an access panel )
On a 2000 Lincoln Navigator : The switch for turning OFF the air suspension compressor is located in the front passenger footwell , by the kick panel
The compressor is located on the front passenger side of the engine compartment just in front of the battery. (man, have we had problems with the whole suspension system!)
Turn OFF the air suspension switch that is located in the right front passenger footwell , by the kick panel
The 2007 Lincoln Navigator has 63.3 in. of front shoulder room.
The 2004 Lincoln Navigator has 41.1 in. of front leg room.
The 2005 Lincoln Navigator has 57.9 in. of front hip room.
The 2012 Lincoln Navigator has 39.5 in. of front head room.
The 2005 Lincoln Navigator has 41.2 in. of front leg room.
The 2010 Lincoln Navigator has 41.1 in. of front leg room.
The 2007 Lincoln Navigator has 41.1 in. of front leg room.