I need help wiring the transformer
I have two black wires coming from unit and only one black from transformer
I don't know which one goes where

Check the transformer output , it should be 24v ac voltage. If it is the 2 wires from your condenser got to the contactor for the compressor in which case as long as one side of the wire don't go to ground it doesn't matter. If it does the one that's not grounded is the hot and should go to the black on the trans former and you need to pick up a common for the other leg .

(guess I should have asked what it was attached to... lol)

Sounds like an autotransformer. These have a common for primary and secondary windings. Sounds odd as most use low voltage control, if switched by high voltage, it would make sense?

You need at least four wires for the transformer to work. Two primary and two secondary. And you have how many??

You need at least 3 wires to work, I think T-Top is thinking isolated coils transformer.
Need Coil Voltage?

My bad I assumed we are working on a normal 115v or 230v system with 24vac out put.

I would think that also, Maybe a wire broke off from transformer?