dual tank question and Hi!

[BorgDog]

Hi, I believe this is my first post here. I picked up a 78 GMC PO made flatbed a couple months ago for a dump/lumber yard/beater truck. Its a K25, Royal Sierra, Camper Special with air bags in the back, and a 350 under the hood. It runs good, rides like a truck has decent tires and suits my purposes just right. Only thing I needed to do was replace a few rotted boards in the bed (replaced them all while I was there) and have some rust around the windshield and passenger kick panel area to repair someday. I also added the side toolboxes from my old truck for storage. Hopefully the picture works.



So I was crawling around under the truck today and ran across this:



From reading on here and seeing what everything runs to, I believe that is my switch for the dual tanks. As you can see, the hoses are no longer hooked up to it and are just run to a "T" to the left of the switch and the single hose run forward from there. This seems to be working, and when I switch the selector in the cab, the gas gauge does change, but I'm wondering what exactly is going on here. Is it literally just pulling from both tanks at the same time? And more importantly if one tank runs dry (or I only fill up one) will it just suck air from the empty tank and I won't go? I'm guessing at some point the switch quit working so they came up with this solution. Now this may work out OK as I was thinking of pulling the drivers side tank and putting an underbed toolbox in that spot and selling my side toolboxes that are taking up bed space. What else would I need to do to remove my drivers side tank besides just connect the passenger hose straight to the fuel line?

Thanks in advance, and hopefully I won't bug you all too much.

Oh, and while I'm here, how do I get the damn Fasten Belts light to turn off?