could also be switch for overhead light bar say for volunteer fire dept... check the roof for any wear marks..
trace the wires from the switch and see where they lead....
could have also been for a backup light...

 

That's what I was thinking, some sort of lights that where attached to the truck.

Great idea about the government lights, it did have a government tag on the back window I believe...will be definitely checking the roof now! Going back today to check on the truck to see if the mechanic has finished the inspection and repaired the transfer case.

 

So what was the switch for? I guess the first person I would be asking is the guy selling the truck.

 

I would stay away from buying it just because of that. Could be some type of switch that was needed if the truck was under heavy load like trailer brakes....