Jay-J, I should have read the question more carefully. I have not found an installation manual for the Aprilaire anywhere online. The closest I have seen is the link I posted, and as you pointed out, it is not an installation manual (not even close!).
I don't like it when companies closely guard the information that their customers need and are entitled to. Aprilaire probably would argue that they are protecting their dealer network and preventing consumers from harming themselves and their heating system, but this is a lot of bunk.
There, I said it and I feel better!
Good luck finding the installation manual -- it may be out there somewhere. --Billy