You can do a single select; try this:
SET TERM || ;
CREATE TRIGGER populate_defaults FOR units
ACTIVE
BEFORE INSERT
AS
BEGIN
select value1, value2, value3, value4
, value5, value6, value7, value8
, value9
from defaults
into new.value1, new.value2, new.value3, new.value4
, new.value5, new.value6, new.value7, new.value8
, new.value9
END ||
SET TERM ; ||
I just can't remember if the new
have to be prefixed by a colon or not, that exercise is up to the reader.