Did ya try putting some fuel in it?
Does the light still work properly or is it on all the time? If the former, check the connector under the tank. Sounds to me like a bad gauge or buggered connector. IIRC the dash light and the guage read the same signal wire (y/wh) so if the light is still working properly then the float is probably still good. If the latter, then the float is most likely the culprit. But I'm no diagnostic expert, maybe others will chime in to confirm.