When we pulled in to San Diego yesterday, I turned on the tank gauges to see how the fuel level compared with dead reckoning. Miracle of miracles, the tank was full. Today, I extracted the fuel sender and saw why. This VDO sender is a simple affair. There's a contact that runs along a resistor. The contact wipes the resistor contact surface except for the part we rarely use... where the tank is below 1/4. All of this is immersed in diesel, but the voltage is low and the diesel doesn't go kablooie. This was an education for me. Fortunately, a fine grit sand paper treatment fixed the problem. It's always something!