You have two issues here: setting up fields and values to properly relate the data in each file and working through the steps to actually link the files to each other.
The first issue is most critical. To link the records in two files via a relationship, you must have a field in both files that stores exactly the same type of data (number, text, date...) and if two records are related, these two fields must have exactly the same value. You can match your records by name to get started, but you'll want to move to matching serial number type ID values as soon as possible. You'll also have to analyze how the data is related, one to one, one to many, many to many? Each type of relationship has its own requirements for getting the relationship and your layouts working correctly.
The second issue is easier. You can link tables in two files just as though they were in the same file once you tell Filemaker how to find the related table.
Enter Manage | Database | Relationships.
Click the new Table Occurrence button. (Leftmost button at bottom of window)
Select "Add Filemaker Data Source" from the data source drop down and select the file that contains the table to which you want to link.
Thanks for this. Sorry for the delay in replying - I have been out of town and had email problems.I will try this approach.