Ok, now that I can see what I'm dealing with, I now know that I'm working on an electric furnace not a gas furnance.
Pretty sure you have a multi-tap transformer that takes only 1 of 3 combinations of primary power (120V, 208V or 240V). The secondary power goes directly to the board.
What are you using for primary power (120V, 208V or 240V)?
Also, can't tell if the fan wire is just hanging loose or is attached to the Y2 (second stage cooling).
Can I get a pic of how the primary wires are connected to power?
At this point your saying that you have primary power but, no secondary power and that the transformer from your other unit works in this unit and the unit heats and runs fine with the transformer from the other unit, correct?