was on my way home from work and my headlights went dim for about 2 seconds and back to normal. did a couple times. now my dash lights are dim. went and got a new battery, but still the same. my battery light is starting to flash now, but truck starts normal all the time. could it be alternator starting to go? it's a 2000 expedition

 

just had alternator checked and was good. anyone have any ideas.

 

Check the positive battery cable that comes from the battery and alternator across the front of the engine compartment to a junction behind the power steering reservoir. It is usually hidden under a black plastic square cover on the driver's side fender well. These cables and connection have been known to corrode and cause problems similar to yours.
The power divides at this point and supplies the power to the internal parts of the vehicle.
If you decide to clean it , its a good idea to disconnect the cable at the battery.
Just remember now you need to give the ECM time to readjust to your driving mode for a few trips since you disconnected the battery. Let us know if this was any help.