Bench testing rally gauges

I know the fuel gauge has ivr in it, I'm trying to see if that gauge and temp gauge is toast. I'm not looking to calibrate, simply looking for needle deflection. I'm using 6v lantern battery, red/positive to "I" post, but should the -ve be hooked to sender/"S" or the "A"?
Pics attached, the 3 post is fuel obviously, the 2 post is temperature.
Thanks
Steve

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