The problem certainly sounds electrical. Your sending unit should have a couple of wires connected to it right on the top of the tank, check those for corrosion, if they are good you can actually pull the sending unit out by removing the screws holding it to the tank, probably half a dozen or so and see that the arm is moving but the fact that it remains on empty is pointing to electrical, there might be an in line fuse and I would check for that, also if there is a fuse panel check those, all those wires sound pretty normal from what I've seen with boat wiring, there is the gauge it self then a wire for the light to it and then the hour meter is probably hooked to it. I would not try to guage fuel consumption by the hour meter, that's a diasaster waiting to happen, too many varialbles in fuel usage for that. A fuel flow meter is a great tool, I have had three of them and they do a lot more than just tell you how much fuel you have used, they will help you trim the boat to get the best fuel economy and performance, I would highly recommend one, there are several on the market, all the ones I have had have been the Flo-Scan and they are expensive, I know that Standard Horizon makes one that is cheaper, NavMan has one on the market and Lowrance is working on getting one out, Mercury and Yamaha also have them in their guage packages. Consumers Marine Electronics in New Jersey carrries several models and if you Google them they have a web site.