When you lock the door with the key from the outside or the key fob ?
Does it have the factory RKE ?
Is there any other add ons ? ( aftermarket alarm, powered running boards, etc )
The 2000 still used the RAP ( Remote Antitheft Personality ) Module with the lock and unlock relays ( in the F-150 these were under the oval on the dash - it is held down with spring clips ).
There are 3 relays, driver's unlock, all unlock and all lock, these are powered by the BJB fuse #8.
Just so they are posted up straight away ( the F-150 power door lock cells )
Not 100% sure if the 2000 EXPY is the same as the 2000 F150 or if it is closer to the 2001 F150 where the locks are directly connected to the CSM ( Central Security Module ).