I don't have the 1999 Manual on this PC, I'll have to take a look when I get home. The following information might get you going.... Also, it might be good to know the Expedition has some years where the code is in the Jack Compartment visible with the Jack removed.
No help at all,
here's your Owners Manual.
Here's what I know about these:
I'm told 1999 is under the dash, above the pedals as well.
The '01 Expedition has a blackbox directly above the brake pedal with a 5 digit # on it..
The '00 Navigator has a whitebox under the drivers side dash with the code # on it..
The '01 Navigator has a graybox under the drivers side dash, way up there with the # on it..
The '02 F250 has a blackbox behind the brake pedal, on the firewall with the # on it..
from another poster:
"the code is taped or stuck on the processor or ecm under the dash on left side by the emergency brake pedsal"
In all cases, the sticker with the number is looking right at you.