You could use a DLOOKUP
http://599cd.com/tips/access/dlookup-function/?key=AlexForumAF
=DLOOKUP (Field, Domain, Criteria)
e.g.
=DLOOKUP ("LastName", "CustomerT", "CustomerID=5")
Or
=DLOOKUP ("Address", "CustomerT", "CustomerID=" & CustomerCombo)
Just set the source/default value of your...