[jocko]

The floor switch you mentioned for the fuel only changes the tank the fuel comes from - i.e. it's just a selector valve - it doesn't have any effect on the fuel gauge. It's entirely possible that your aux tanks were never set up with fuel senders, so the gauge always indicates the cab tank level - but some aux tanks did get senders and, in that case, the gauge was normally controlled by a 3 position toggle that only affected the gauge display - didn't switch the actual fuel source like your floor switch. If it's a 2 position switch, probably just for the fog lamps you mentioned.