Technical Early Ford fuel gauge incorrect with new sensor

The original '36 Ford fuel gauge with the stock sender read OK at first, when fed 6V through two Echlin VT6187 voltage regulators in series from the 12V source. Once a Classic Instruments SN39 fuel sender was installed (10 – 73 ohm for early Ford gauges) the gauge needle pegs at the top with any fill short of almost empty. Putting 17 ohms of ballast resistors in series in the 12V power feed (replacing the Echlin regulators) gets the gauge to read accurately, but that seems like a really high resistance. With that resistance (tank sender and ballast resisters) it’s seeing only about 0.4 amps. I’ve checked the wire to the sender and it show no shorts, and running a new wire gets the same results. Any thoughts?

Steve

 

I think you got the wrong sender for your gauge. All the gas gauges that I've ever run used the 6 V sender deigned to operate that particular gauge. There is more than one way to drop the 12Vs to 6 to make it function correctly. I've never had any luck with mix matched parts. I have a 6V SW gas gauge in my truck. It works fine because the parts were made to work together. Get the right sending unit for your particular gauge and then step the voltage down and it will work fine.

 

The stock sender has by design a 10 - 80 ohm (approximate) range, and this Classic Instruments sender is reading (mounted in tank) 20 ohms with just over 3/4 tank. The sender is strictly a variable resistor, it should read correctly with the stock gauge.

A replacement early Ford sender needs an adapter ring to mount in 'Tanks' brand fuel tank. and the float arm would need extending/rebending. But, the SN39 sender is the normal replacement for the 80 year old OEM part.

Steve