Early gas sender unit question

[Chris Marshall]

What is the operating ohm range of the early (pre-war) Ford gas tank sending units and corresponding gas gauges?

0 - 90 ohms?

240 - 30 ohms?

I actually have a couple NOS gauges, but they are not marked as far as operating ranges.

Thanks, Chris

 

[Kurt in NJ]

The original senders are not the same as modern senders, they do not change "resistance" like a modern sender, they change the amperage that the gauge gets, inside the sender is a set of points, a bi-metal strip, and a heating element.

Changing the float level moves the bi-metal strip, which closes the points tighter, the points being closed turns on the heater. The heater in the gauge that makes the needle move is in series with the heater in the sender and mirrors the senders movement.

This is why the repros that just use a resistance do not work very well with original gauges, most "modern" cars (pre electronic) had an "instrument gauge voltage regulator that was a bi-metal strip with points and a heater to regulate the electric for the gauges, on our old fords it is built into the sending unit .