on my 1972 Chevy van, the previous owner installed an extra gas tank but it had no sending unit so I could not understand how it worked. until I crawled under the van to fix the main tank and saw the electric fuel pump that had died. I guess the extra switch on the dash was for when the main tank got low you flipped the switch and pumped gasoline from the Auxillary to the main tank to refill it. the problem is most of the 3/8 hoses were rotted off so I have to figure out the routing and replace the hoses and filters the main tank is rusted and the sending unit was stuck on 3/4 of a tank, I thought I was getting good mileage until I ran out of gas after changing the mechanical fuel pump it still wouldn't start so I tapped on the tank and it was bone dry. got the main tank out and am trying to find a sending unit. what other years will fit? the engine has been rebuilt except for the rings and camshaft but they are next.