Ok lets see if I can explain.
I want to make a query that will set criteria based upon entries in a table. So, let me give you some data to play with.
Table1 - field1, field2
row1 - l2a1234, Y
row2 - l2a2345, Y
row3 - l2a3456, M
row4 - l2a4567, N
Table2 - field1, field2, field3
row1 - "Y"...