This Positraction is not a selectable locker. This part number is simply a clutch-type limited-slip differential, and while this kit will lock when one rear wheel starts to slip at a given torque value, it's not a truck selectable locking differential that will just allow you to keep your differential totally locked at will. If you're looking for a true locker or E-locker, give us a call directly at 1-877-578-2433.