I replace the battery and alternator on my 1999 Ford Expedition and the battery light is still staying on

SOURCE: 1999 Ford Expedition Interior overhead lights stay on, door locks

locate the relay for the interior lights and doorlocks and replace it.

Robert

SOURCE: 1999 S10 battery light stays on

could have a loose wire did you check your alternators output voltage? if it's 13 to 14 drive it, as these have internally mounted voltage regulators

SOURCE: battery indecator light on on dash

Check to make sure that there's power from the alternator to the battery on the charge-back wire. If nothing's there, then your alternator is junk and you'll have to replace it again.

SOURCE: 03 ford expedition interior lights stay on and door ajar reads

This is a very common problem with Fords. I have one that was doing this as well. What works for most people is pretty much what you have tried - spraying inside the latch all over with WD40 Until it's coming out the bottom of the door. If this fails to work, the switch probably needs replaced. The switch is located inside the door near the latch. It should be pretty easy to find once you have the door panel off. Look for the wires leading to it. A new switch is usually very inexpensive, but may have to be purchased through your local Ford dealer. If you're not comfortable taking the door panel off, a mechanic should be able to do this repair for you in less than an hour of shop time.

SOURCE: 1999 Ford Expedition - fuel pump not working after replaced alter

replace the fuel pump