I recently removed the rear fuel tank from my truck because it was rusted out and leaking. My question is, should I plug the fuel and return line or should I plum them together in a loop. Will not having the second fuel pump plugged in cause any problems?

 

I would plug the ends of both lines. Better yet, if this is a permanent fix, I would only connect one set of fuel lines to the tank. You don't want to suddenly develop the cross flow problem with the other return line dangling under the truck.