It's been a long time since I did this, but I do remember a little.
There are 2 different types of IAC as I recall, and the wiring depends on which of the two you used. In my case, I had 2 different throttle bodies I was working with. One had a GM IAC, and one had a Chrysler IAC (I think my Holley TB had the Chrysler unit). Anyway, the wires had to be reconnected depending on which setup I used.
So start with the question "Which IAC am I using?", and go from there. Ensure that the IAC and wiring pattern match. Again, it's been a while, and Jody has more experience with these than I do, but I want to say that if it's wired wrong, it would go full open or full closed when you power up the ignition, so perhaps you can look at what it is doing before starting the engine?
Good luck!