Trouble with gauges

Kannon Herbert said

I’ve also noticed that 20dbl isn’t getting any power in any key turn position.

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G5 20dbl has to supply 12 volts to the limiter, the brake warning lamp, and oil warning lamp, with ign' switch in run position,,, so that is your problem. You'll need to trace G5 back to its source. I don't know if this is fused in the later models but I know it wasn't fused in earlier models.
As for the 'A' and 'S' on the back of your fuel and temp gauges, 'A' is altered or adjusted voltage in, 'S' is sender or signal. when testing gauges outside of the panel with a 3 to 5 volt power supply, which is which wouldn't matter. Current from post to post generates heat, heat bows the bi metal beam. That beam wouldn't bow backward with reversed polarity.