The electric locker would be a PIA to install, as it tied into the ECM/BCM, speed sensor even on 2WD's. Perhaps the PO thought he needed switch and went ahead an popped it into the dash opening, or added it to try and fool folks. Could have been trying to attract that certain breed of woman who will only throw herself at a true MAN; one with a locking diff

, as any other would only father her inferior offspring.
One thing to do pertaining to the diff, the electric actuated diff has a rather large motor or solenoid on the front of the carrier housing, versus the open or limited slip looking normal. If the dealer paid more for the truck on the assumptions that it had more options than it does, that does not mean You have to. It is worth what it is worth.