I'm trying to help a friend on a Fairchild restoration

It has an undocumented carb air temp gauge. Looks like an AN
type indicator-- cannon plug with 3 pins, A, B & C. The pointer
has no zero position so I think it's a ratio measuring device
like many fuel gauges.

The sender is a resistance device with two pins.

I have a hunch one of the three pins is A+, one is ground,
and the third goes to the sender, with its other pin grounded.

There is continuity between two of the pins on the indicator.
The 2K range of an ohmmeter will drive the indicator full scale,
direction depending on the polarity.

So maybe I can figure this out. Does anyone have the answer to
save me the trouble? Surely I'm not the first.

Thanks, Bill Hale