When you do a relational find for anything that does not have a link that shows up in the Find Related dialog box, then you must explicitly provide the link fields. A good example of this is when finding Ledger records in a report, starting from, say, Account. There are no Find Related links for the Ledger file because there isn't even a list where you can view the Ledger file.
will not give you any results.
This is the correct way to specify a relational search from [Account] to [Ledger], explicitly specifying that the linking fields are Code and AccountCode: