12V 5-pin changeover relay  Ref: CLS0191

The contacts are numbered 87 - 87a - 85 - 30 - 86 85 and 86 power the relay through a switch and a 12v supply. 30 is common and typically connected to a 12v power supply 87 or 87a carry the supply from 30 depending on the state of the relay (on or off)