Okay, I've just found out that on the Multiplus 2 K1 is actually an open collector rather than a relay like it was on the Multiplus 1. The open collector is to me a confusing device but it appears it can serve the same function that the old relay used to, with a bit of work.
It seems that open collectors are suitable as an on off switch for a circuit, and that I need only to connect an external relay and power source. And that K1 can be programmed to break and close the power circuit to the relay.
I've read some posts saying that a diode needs to be included in that circuit or else the transistor in the open collector will fry. I don't quite understand why...
Does anyone have an example wiring diagram of how to use the K1 open collector to control a relay?