1998 Ford Expedition electrical draw

Check out our article on this common issue at https://www.2carpros.com/first_things/why_is_my_car_battery_dead_over_night.htm

Already did all of that

If you went through those steps already and found nothing then there must be a short in the wiring. Not a easy task at all but you will have to go through the vehicle's circuitry testing for shorts / damaged wiring.

How do I go about that

Start with checking the battery cables and make sure they are clean and tight. With a volt meter and the car running check the voltage output of the alternator by connecting the meter to the battery. The reading should be between 13.5 and 15 volts if the alternator is working properly. If not the alternator needs to be replaced. If the alternator is good then you may have a short or drain on the system. You can check for a short /drain by connecting a 12v test lamp (in series) between the postive battery cable and the postive terminal of the battery. When conducting this test make sure everything is off ( doors closed and hood light disconnected) or you will get a false reading. If there is a short the light will light brightly. A dim light or no light is normal.

Then whats next. Alternator is brand new