how do I use the relay control?
Connect the relay between pin 4[switched] and 3 [ground]

pin 4 "Orange" does is send a signal out is so how many volts?
It´s designed for 12V relays - but be aware, relays should be the low power type to not destroy the contact.
Search for 'Finder 43.61' or a equal relay (12 VDC /580 Ohms)- it´s a good solution