only the driver door unlocks, front passenger and both back doors will not unlock. I have a Fob and both unlock switches will only unlock driver door. All 3 will lock all the doors but only the driver door unlocks
It sounds like this could be an issue with the unlock relay that switches the polarity for unlocking the non-driver's doors. There is a separate relay for the driver's door for the "Priority unlock." Since the fob doesn't work to unlock the other doors the issue is probably not a broken wire in the accordion boot between the driver's door and the cabin. The remote keyless entry system does not rely on those wires for the other doors.
I'll have to check the service manual to determine if the unlock relay for the other doors is built in to the remote keyless module or if it happens to be separate.
Per the factory wiring diagram for the 2001 Sport Trac there are 3 relays for the power locks, and all three relays are located in the Auxiliary Relay Box #3. There is a Driver Door Unlock relay (K131), a Door Unlock relay (K129), and a Door Lock relay (K130).
It appears however that the driver door unlock relay is ONLY activated by the Remote Keyless Entry module, so since the driver's door unlocks with the Fob or door switches, that indicates the Door Unlock relay AND Driver Door Unlock relay are both working fine.
About the only place you could have an issue would be with the splice from the unlock relay to the liftgate lock and passenger door lock. Looks like you might get to go wire loom fishing to try to hook the pink/orange unlock wire.
You might need to check the owner's manual to see if it explains the location. If you don't have an owner's manual you can download a PDF of it here.
The service manual only lists the location for the Sport. I suspect it's different for the Sport Trac. For the Sport it lists LH rear of vehicle. For the Sport Trac that would put it in the bed, I doubt that's accurate.