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Put the key in the Ign. open the door, crawl under the dash about below the ashtray area. It is a black plastic box amongst the wires about 2X3" you should be able to locate it by feel, sound or both.
Just unplug it. Nothing will happen except silence and a dead battery or two (2) when you forget to turn off your lights.
Get a small springy piece of metal. Drill a hole in it. Get a drill screw. Place the metal so it will hold the door switch down and attach with the drill screw. Then you can just rotate it off the switch if you want to use the door switch.
That way you can get in and out of the cab without giving yourself away with the light also.
or you could just pop the pin out of the connector for the door chimes, then the chime will still function when the lights are left on by mistake or the keys are left in the ignition....