My 05 TJ is the first 4 wheel drive vehicle I have ever owned, so please forgive my ignorance. What does a "locker" do that is different than 4 wheel drive? I thought that when I put my Jeep into 4 wheel drive, all 4 wheels were under power. If so, what does a locker do that is different? Thanking you in advance for educating a newbie. This site is a wealth of info!