There is obviously more than one issue here, but the lights thing is telling you electrical, not fuel. Yes, the fuel issue needs to be addressed also, but that isn't causing the electrical problem.
I used the Kreem product years ago on a previously uncoated tank, and other than the fact the stuff rapidly turns color in use to an ugly brown it worked fine. It's a bigger PITA to apply than the literature implies, but it does seal the tank. The question I would have is how do you intend to remove the existing sealant first? You won't want to install a new layer of sealant over the old peeling stuff, unless you want it all to continue peeling. The new stuff needs to bond directly to the metal of the tank.
Jerry