The post just goes through the plate to a metal strap, as long as the two are connected it will work, however if you grounded your (that post/strap) + side, you could have blown the gauge.
Gauge Test w/o sender, actually when you ground the gauge + side, it should read full, the only way to know if the sender is working is to either put gas in the tank, or pull the sender, reconnect + & ground, and lift the float as if you were filling the tank, then you will know if the sender is working, as long as you know the gauge is good.
