Auto Fill connected data?

So, I want to automatically fill an object value with a value from a connected object.

I have the following:

A year table with the years in it. This is used so I can manage connected object drop downs in the form so I can present data base on the year of the main record.

The main record has a year connection to the year table. When a new user arrives, to insert a form, I'd like it to automatically attach to the highest value in the year table.. I have set the year table to sort by highest to lowest.. I've set the field to use the default value, and I've hidden the field from the user, since they don't need to see it.

However I can't get the value to be put into the record. How would I do that??

I also have the same problem with the tax field. I have a tax object connected to my main object. There will always only be one result, since it's based on the year of the main object and the location selected. But it does not seem to want to actually put the value in the object record.. Again this field is hidden since the user isn't going to select anything..

Soo, what am I missing??