Ditching switch
I cannot tell you what the ditching switch does on the A320 family of aircraft. However, I do know that it doesn't activate the Automatic Fixed (AF) ELT. Other than activation by the "g" switch, only other activation is from the control panel in the cockpit. Normal position on this switch is armed, after lifting a guard it can be moved to reset or on.
Without going into the exact parameters for the "g"switch I can advise that a simple way it is tested by avionics engineers is to hold the ELT like a rugby ball and do a gentle "dummy pass". This is sufficient to activate the ELT, hence my reason for stating in an earlier post that even a controlled ditching would generate sufficient longitudinal de-acceleration forces for it to activate.