Where are suspension airbags located on 1999 ford expedition Eddie Bauer so I can check for leaks?

Hoo boy. Sounds like you already have some leaks. Please know that this is a sign of things to come. Once one air bag starts to go the rest are sure to follow...then the air lines...then the solenoids...you get the idea. You can save yourself the money and hassle and just switch over to good old coil suspension, which you probably won't ever have to think about again for as long as you own the car. Give these guys a shot:

4x2 has rear air spring only. 4x4 might have front air spring. on the front it is a coil over type arrangement. on the rear its an air bag beside the shock absorber. use soap and water to check for leaks including the plastic air lines going to the front right side of the truck. that is where the air pump is located

Front or rear ? Either way rear are on axle just inside leaf springs and the front should be just in from tires going up to inside wheel well .