it is the port for a disable key. you remove the key to disable and just plug it in when you want to drive off. the dealers put those cheap ass things in in hopes of selling it to you as a theft deterrent. if you opted not to have it, they break off the plastic part off in there and you can drive it. if you get a pick you can pull out the plastic and your truck should not start. you can just yank that crap out.
Wow. Seriously? I've never heard of this. That's totally half-assed and stupid.