toggle switch - what's it for??

look factory or PO installed? fuel heater?

 

Go ahead and laugh but maybe it's a panic button when hooked up it sends a warning to your company something is wrong.

 

Activates the bat signal?



Best way is to trace the wires and see where they go.
The only two factory switches that I've seen in that spot were for the passenger window and rear work lights.

 

IH was close . when you flip the togle switch it activates a Force field around the truck, preventing lot lizards and people that have run out of gas from Knocking on your door. Thats why you dont hear anything.

 

I drove a '96, it had a night light for the floor. If that's what it is.
Or do you mean the switch itself lights up?

 

Maybe a utility switch for lights or a trailer accessory or something, take a test light to your jumper cable and check it for power while having someone turn it on and off.

 

Could be a dump valve for the rear axle of the spread on the trailer suspension. I have one like that.