Hoi Ronald,
Do you have anything like a universal multi meter to check your connections while NOT conected to the mains.
If you have, you can check the connections by connecting the meter over the N on the input to the N on the power supply.
Only when the power switch is on and the emergency button is not pushed in you should measure a low ohmic connection ( something below 1 Ohm )
If the power switch is of OR if the emergency button is pushed in, you should have HIGH Ohm value ( real high so above 1Mohm )
The same for the Live connection.
Using a 1/4 inch plug is a good idea, and yes connect the - connection to the ground terminal and use the central point for the connection to the input 4 on the Gecko 540
You will use this to check the point height of your cutting tool. The - connection should also be connected to your machine ground.
the tool should slowly decend to the touch plate, and when in contact will know the hight ( relative ). So when chane a tool, afther tool heght measuring. it will be at the same hight to your working piece