Pins 5&6 provide the DC 'ground' (common) when that output is turned on. You need to have the +side hooked up to the other side of the relay. If you are using lower voltage relays you need to power them with a lower voltage supply as shown in the gecko docs.
To make it easier on folks using a single 48V supply I just started carry a 48VDC relay kit. It comes with the relay and terminals to hook it up.