What is this switch? 1983 ford ranger?

I have a 1983 ford ranger I picked up recently. I took the bench seat out to replace it and there was a interesting switch that led to a valve under the car, I didn't look at it very thoroughly but it looked as if it went to the fuel lines, I do not know what this switch does. I twisted it and it turns 360 degrees but every 90 degrees it clicks, can someone please help? I do not have the truck at the moment and it doesn't run at the time so I can't test anything at this point in time.

Sounds like a selector switch for auxiliary fuel tank. Or tanks

Yep. It's a selector switch for a second fuel tank. Two of the "click" positions are OFF and the other positions determine which gas tank you will draw fuel from. Also note that your gas gauge MAY NOT show fuel level in the second fuel tank, so you COULD run out of gas in one tank while the gas gauge is still showing fuel available.

Is it a cut off switch for anti-theft. I know folks that have installed them, never inquired as to how/what.