Don't do this....
 

Just a heads up. The other night I had turned my ignition to "on" so my wife could see the gas mileage. When she got out of the truck the key was left in the on position. My headlights are always set to auto, so when it got dark the head lights came on. Fast forward a few hours (4-5). I went outside to make sure everything was locked up and noticed that the trucks headlights were on, but dim. I got into the truck and tried the key, noticed it was in the on position, opps. Nothing. So I tried to shut off the head lights, no go. The head lights stayed on no matter where the headlight switch was positioned or the ignition. There was no way to shut them off. Apparently everything is controlled by a computer and with out enough power it shuts down. As soon as I hooked up a battery charger the lights turned off and everything worked. I let it charge for a while and it's fine now.

So, don't leave your lights in auto mode and your key turned to "on" or your truck will end up in an endless loop that will drain your battery that you can not get out of without external power.

Not that this chain of events should every happen, but it sucks that once the battery has drained enough, you can not turn off the lights.

BTW this was on an ’06 Lariat Screw, 5.4

thx for the heads up, i have a 06 screw too. and i always leave the keys in it too but in the cupholder lol.