I have often struggled with this in the past and keep forgetting what I did so I thought I would post this to help others and myself in the future (getting too old…)
When Editing a multilayer terminal in a schematic, I want to associate up to three terminals but the method is backwards from what I expect it to be. I though that, if I edited a terminal, I would associate the level I want to put the other terminal into. That is not the case.
For example, if there are two terminals, 1 and 2, and I want to associate terminal 2 so that it is and the middle level with terminal 1 on the top level, I edit terminal 1, select Add/Modify, and then I pick Terminal 2 from the select Association window. Now select the middle level of both terminals, click Associate and now both terminals are associated. You might have to move the numbers up/down to get them on the appropriate levels. (If you set up terminal 2 so that it is already on level 2 then it associates to the appropriate level. If both are on level 1 when you start, then level 1 will have 2 in it and level 2 will have 1 in it in the top window when you are done.)
It confused me for a long time because I would have thought that I would select the level I want to associate the picked terminal into the terminal I was editing, not selecting the same level in both terminals. (i.e., the middle terminal in the top window and the top terminal in the bottom window).
This only applies for terminals that are are different pages because using the Pick button for associating works great when the terminals are on the same page. Start with the terminal you want to associate and select the terminal you want it to go into. (i.e., Edit Terminal 2 and pick terminal 1 will place terminal 2 in the middle level or the bottom if the top and middle are already filled))
This is not explained anywhere that I could find. I hope this helps others who may have had the same trouble I had.