Rover 45 fog lamps not working

My 45 has its MOT tomorrow. I checked the lights and neither rear fog lamp is working. When the button is pressed the tell-tale comes on. It goes off when it's pressed for a second time The F20 fuse and the lamps are fine. There is 12V on the red and blue wire but not on the red and yellow wire to the switch. Before someone asks I'm doing this with the ignition switch in pos II and the headlamps lit.



The horn, lights-on alarm, hazard lamps and everything else as far as I know all work.



Question: Is this a sign that a relay in the multifunction control unit has failed? If so, how does the tell-tale get lit as the switch is non-latching? I can easily get a new MCU from a scrappy- is it just plug and play?



I know the garage well so I can take the car and have the rest of the MOT done - it will be no problem to bring the car back later, before the current MOT expires, to demonstrate that the fog lamps work. But first I need to know how to fix them!

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