[jaybutter]

I believe that the reserve light comes on at engine start for a bulb check, like all the other warning lights do. If you don't get a reserve light at that point the bulb or it's wiring is bad.

The fuel level sensor float actually has contact pins on the bottom of it that complete the low fuel circuit when the fuel level is low enough. When I had trouble with mine it was because there was a pile of muck at the bottom of the gauge tube and the float could not get low enough for the pins to make contact.