The PLC project is coming along nicely. It lets the relays be controlled by 2-wire circuits in place of the original 3-wire design. Any combination of momentary and maintained-contact switches (including standard toggles) can be used - they all work together like a conventional 3/4-way installation; i.e. each time any of the switches is operated, the relay changes state. The momentary switches can be paralleled, but of course each maintained-contact switch needs its own PLC input.
The PLC program also implements a Master ON/OFF function, emulating the GE "sweeper" or its ancient ancestor, the "motor master" controller.
