TDBGrid - Linking

I have two tables; Customer and Unit who are related by a CUSTID field.  I
have used Master/Detail to link these two on a DGGrid.  The Customer being
the master shows 7 records, while the Unit Grid only shows a single record.
I'm new to builder so I'm certain I'm missing something simple, but how do I
get the Unit Grid to show multiple records as well.  Seems like a fairly
normal application.