Cbking

I just bought a 2009 Screw 6.5 foot box Fx4 5.4 and i have a few questions manily on the rear locker. I was reading that you can't lock these trucks in 2 wheel drive but yet my switch pulls out in 2 wheel drive and locks. did a previous owner put in a raptor switch? I previously had a 2004 Lariat any thing majorly different that I need to know about this truck? Thanks for your help. I hope I can become more active in this community as I learn more.