Siemens PLC (programable logic controller) wiring to its outputs. Yellow cables to the inputs. I have a dozen of these to wire up... and they're talking about buying another six. It's not just the wiring, they need mounting on boards with a mains power supply each, and the most awkward bit will be finding a way of covering up the mains wiring and connections to ensure they're safe for folk to use. Thankfully, as I'm busy with other stuff, there's no urgency to do these, so a chance to come up with some ideas before they're required next year.