Johnson Pump Automatic Switch For full automatic bilge pumping operation, connect the automatic switch to your bilge pump. Switch has a time-proven micro switch without mercury. When water exceeds the acceptable level, the pump is turned on by a rolling steel ball, which changes the pressure on the micro switch. Attaches to any Johnson Pump bilge pump through the clip on "T-slot" and can be used with 6, 12, 24 or 32 V systems.