I have a customer that wants a loud bell connected to a DX 120. I have a Viking unit PA-2A with horn. It works when I plug it into the analog line ports on the Viking unit and spliced to the carrier and system. I can wire in a night switch to turn the loud bell on and off for use during the night and day and it works fine. However, if I try to wire to the loud bell port, program a button 779 on the phone, to toggle on and off, I cannot get this to work. Any ideas????