[tomvv11]

Thanks indeed. I've repaired the other end of these wires before but this is next level reverse engineering. I'd thought it was a simpler mechanical switch on the float.
Does the slotted brass ring sit on top of the inner small diameter white tube that the magnet slides along?
My reserve light comes on very consistently after 3.5 gallons has been consumed. The tripmeter/3.5 tells me fuel mileage and I can then determine exactly how much range remains.
Having blown it once uphill from a gas station I know my tank's capacity is 4.931 gallons, but I call it 4.8 to take pump inaccuracy into account.