Fair play you have spent more time and energy working on a system that took me many years. Most of the vessels we own or supply are deep water moored and an efficient bilge system in force 9 plus is of significance to the point that we always fit a twin bilge with independant batteries.
Auto systems tend to work on various number of principles
1. A merc switch
2. Mechanical ball switch
3. Earth resistance
4. Back pressure sensor.
One of the important points to any system is the delay in detecting a water level and the intruction to start pumping. This is why we like the computerised method as it avoids false starts in a heavy sea.
After many years we have found the Rule 2000 and 3000 computerised systems the best and they work on back pressure sensor. Of over 50 supplied we only last week had the first one returned. Of caution though the filter in the base must be checked on a regular basis and the major failure with all pumps is human hair---- it falls onto the deck, goes aft into the well and when spinning round the pump makes a very strong rope. So every so often turn the pump upside down and pick the hairs out !!..... dont let your wife do it in case its not the same colour as her hair !!!!