Most of the searches are categorized, so withing the group/search/ directory there is a place to define the various kinds of searches.  For beam searches, it is beam_searches.ml.  The new search has to be added there.  This is the code that makes the call to the solver. 

There are also 3 files called:

alg_table_dd.ml

 - for algs that drop duplicates

alg_table_dups.ml

- for algs that track but ignore duplicates

alg_table_nodups.ml

- for algs that don't even think about duplicates.

The code in this table calls the code in the aforementioned file, based upon a string name.