I have a sine-wave inverter manufactured by Power Conversions P/L in Victoria. It is the "Slimline" series, 500 Watt. According to the current operators of PC, this was made by the previous management something like 15 years ago and they have no info on it.
On the rear panel is a 5-pin DIN socket, which apparently is for I/O functions - remote on/off has been suggested. (One interesting characteristic of this inverter is that if the DC input CB is opened and reclosed, the main [output] on/off switch has to be cycled to get the inverter to restart.) I have traced the DIN connector circuitry and it drives a pair of 4N35 optos.
Unfortunately exciting these optos doesn't cause any change in the device - if on it stays on, if off it stays off. If the "remote" function were to over-ride this it would make some sense.
I am hoping that someone out there has info or history on these and can shed some light.