Add new record to subform using custom input form

[Ashleyjp1985]

I am working on a database for storing customer information The basic structure is:

CustomerDetails Table (PK CustomerID, unique number) with a one to many relationship to CustomerBuisnessLines (PK BuinessLineID, Autonumber) linked on CustomerID with a one to many relationship to CustomerBusinessLinesInteraction (PK InteractionID, Autonumber) linked on BusinessLineID

I have created a form that displays CustomerBuisnessLines and then in a subform displays Customer BusinessLinesInteraction. Through the datasheet view i can add a new record to the subform.

I have created a separate form that allows the user to view and add records. it is accessed by double clicking on the subform InteractionID field on the datasheet. It displays records fine but i cannot get the form to pick up the BuinessLineID to link it to CustomerBuisnessLine when adding a new records it just creates ophan records.

Any advice?