Welcome, Jack. The low fuel light is triggered by a thermistor in the tank. It changes resistance as it gets warmer from being covered with less fuel, so the fuel light barely begins to glow until as the fuel gets lower it will be at full brightness.
Sounds good, right?
Unfortunately, the electric petcock has the same connector, and if they are hooked up backwards and the fuel is low, the thermistor burns up. Not good. There is a yellow stripe on the matching pair, but it many times goes unnoticed.
To test the light, jumper the two pins with the ignition switch on. The light should work. To test the thermistor, check ohms between the two pins. I don't remember the value.. I'm old.. but if it's either shorted or open, it's toast. They're not cheap, but should be ok unless someone has reversed the leads.