Not sure what I am doing wrong here, the building is connected to a large power pole, power is set to input but nothing inside is receiving power? I have over 400 steam engines running, and using around 30% of my power.

Edit: Added screenshots: https://imgur.com/a/cSLAu

Are the inserters connected to the power pole inside (do they show up in the inside electric network)? Disable your other mods and reload your file (don't save), then tell me if the inserters are still flashing.

Wow testing whether or not disabling mods might help completely eluded my mind, inserters work with mods disabled. They were not drawing power from the power pole inside the building before. Testing now what mod might be the issue.

Ok, found the culprit. It was the Full Power Coverage mod. Sorry for troubling you.

No problem. That mod has caused issues before.

Is it, at all, possible to make it work with "Full Power Coverage"?

or use the patched full power coverage mod https://mods.factorio.com/mod/Full_Power_Coverage_Patched_For_Factorissimo