Custom Function map() to lead lookup field

Custom Function map() to lead lookup field

"Client" is a leads lookup field within my custom module, what does "leadID" need to be in order to associate the lead with the new module?
    1. field=map();
    2. field.put("Client",input.leadID);
    3. response = zoho.crm.create("CustomModule2",field);
    Given a lead, how do I map it to a lookup field in a different module?