It seems this should be simple but I can't figure out how to do it.

Dr. P has a DB of accounts, Dr. J has a DB of accounts. The third DB is personnel. I use the Personnel DB for informaiton and processing payroll. Staff can be funded on both Dr. P's and Dr. J's accounts. I want to plug in the account number on Personnel and have it search both account DB's for the related information.

I have a relationship of account number to account number for Dr. J's accounts and it works fine.

How do I make one field check 2 DB's for information?

It's better to have all accounts together in the same table. You can still restrict access to particular account records based on the current user, and this solves your search problem.