Is it possible and how hard is it to add a switch that will kill the interior lights when a door is opened or the truck is turned off.

Thanks

 

So you want the door switch to work opposite of what it is, or if the truck is not in the accessory or run positions, you do not want the lights to work ?

 

What exactly are you trying to accomplish? A stealthy exit, like cop cars? Just cut the wire from the driver's door latch switch & insert a cheap switch. When the switch is ON, the circuit will behave like stock. When it's OFF, the LCM won't know when the driver's door opens.

There's a VERY slim chance that your LCM would respond to the police configuration (Dark Mode) described in this caption: