Cutting the wire would be my last resort. Unscrew the sender (after pumping and flushing the tank a bunch to make it nicer). There is a vent hose and 1 connector on it. You can then take this out into a bucket and clean it up.
Using a digital multimeter (they are now cheap enough everyone should have) you can beep out the floats using the continuity function. Plenty of youtube videos out there on how to check continuity. Then you can find the pins for each float, move the float and see if the continuity changes state. I believe the empty (longest) is normally closed, meaning when the float moves up it actually opens. The rest are normally open, when the float moves up they close. Only if you can't get it to show closed on the multimeter by manually moving the floats would I cut a wire. The actual switches I believe are magnetic reed switches inside the float tubes.