The problem shouldn't be related to the fuel level sensor/float. Those will be the two smaller gauge wires at the pump module plug, most likely a purple wire and a black wire.
I'd reconnect it back to factory to verify the issue is related with cutting power to the fuel pump. Maybe you blew a fuse somehow. I don't really believe there are any cross circuits that share the power of the fuel pump grey wire or anything that depends on the fuel pump working. Should be the same scenario of when your in tank pump dies but the gauge still works and tells you how much gas is in the tank. I don't think it will give you a different result but you may try hooking up the grey power wire and cutting the heavy gauge black wire which is fuel pump ground.