Lights out on command O72 switch controller

It comes apart easily. Four little screws and you can measure the continuity of the four wires to the little circuit board. Probably one of them came loose inside? Did you measure the wires into the controller itself? Even so, the parts are simple and replaceable. Maybe a solder joint inside became intermittantly as well.

Not much to them, it'll be obvious when you open it up.

I opened it up and nothing unusual. I decided to swap it out for a controller from a broken switch. All is good. 

Since it's not likely that two resistors and/or diodes opened up, then the most likely fault has to be either the yellow wire, it's connection, or the black wire or it's connection. If the controller works to switch the switch in spite of the lights being out, then it's most likely the yellow wire connection somehow. Broken yellow wire (inside the insulation) or bad solder joint where the terminal block is soldered into the circuit board.

So simple a device, it's interesting as to why all the lights are out, eh?