I have a 1996 Ford F-150 and I just replaced the lock cylinder. Everything works fine, however, a alarm chimes when the key is out of the ignition, the headlights are off and the driver door is open, it stops when the driver door is shut. Is this normal? Or is the key warning switch faulty?

 

Yes, it's normal when the door is open. It's there for the purpose of alerting you that the door isn't quite shut or you left the lights on.

 

no that is not normal. it is supposed to chime if the key is in the ignition when you open the door to let you know the key is still in the ignition so you do not lock it in the truck.

there is a little tab on top of the key cylinder that is not aligned properly. most people just disconnect it because it is a royal pain in the butt to get properly situated

 

Is there a diagram of this switch somewhere? Mine chimes all the time and drives me nuts

 

probably, but easiest thing to do is get rid of it.
There is a module that plugs in under the dash almost right above your right foot and transfer case if sitting in truck, you cant miss it. unplug that and no more chime and its the best for tailgaiting with stereo on and doors open.
just make it habbit not to leave lights on or keyes in. the chime wouldnt help most people with the issue of locking keyes in truck, that would take a whole lot more

 

I'll look for it later. I like to leave my doors open sometimes when I'm working on stuff. My switch just spins loosely and it has to be in the perfect spot to get it to quit dinging.