What really happens on a dual tank truck when the back tank is not working?

[alaman18_2]

I just got a 1988 Ford F-150 Lariat L6 5 Speed standard with dual tanks. I fill up the back tank and nearly filled up the front. I drove it for about 150 miles mostly on the back tank. I noticed that the back tank stayed on full the whole time. Later I go to switch back to the front tank and guess what? Yup. The gauge dropped to about a quarter tank and the back is still full? I've just fixed the truck from stalling out. It has a new fual pump, new spark plugs, new rotter, and when I replaced one of the two relays, it finally stopped stalling and I can actually hear a pump when the key is turned on. Could the other relay be bad causing it to only use the front tank no matter what the switch is set on? I have to get the other one from the dealer because I can't find it at the parts store. If that one's replaced, will it start using the back tank too and was it really using the front the whole time because the back was failing? Do they do that? That's scary if this is true. I wish there were a way to take it out of the back and fill up the front. I guess I'll have to use the front tank only for now until I can fix the back, but I think the front is smaller not sure. I just wanna know if it can actually automatically switch to the front without you knowing it if the back one fails. I think it's just telling me what's in the back but not using a drop of what's in there. Is this true?
so what does this mean?
what do you mean buy starving it. is the bck taking fual from the front when i switch it over. would it go back into the front tank if i switch it over to front for awhile?