Where does the black fuel sending wire go

Unless you have chopped up the harness, the sender wire connects when you plug in the harness connector

Not intimately familiar with the "rear" of those cluster,s but I believe it's the pin right above the "key" in the connector

The condenser can stay or go, it is for radio noise suppression/ filtering

In other words the three fuel gauge terminals are:

The one with the black cover is the OUTPUT of the IVR, and comes out to feed the other two gauges.

The one with the cap is 12V into the IVR

The third is for the sender which leads directly to a connector pin