1. Don't put the sender back in until gauge works. It is THE tool you need for bench testing.
2. You say you connected it externally and nothing happened. That would depend on how you "connected" it/tested it.
3. If you are unsure or not acquainted with electrics, Don't hook anything up until you get instructions here. You will damage something.
Watch the vid and read the link to get up to speed.
Click
And Clack

Ask further after reviewing, or report results. It is going to be a ground problem or the gauge or the sender. Does not matter if they "look" good.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn