MC radiator fan started coming on after turning car off

[Cooper69S]

Hi all
We've have a Mondeo MC diesel for about 9 years and late last year the radiator fan started coming on after the car is turned off. It runs for about 10-15 seconds then turns back off again. No other issues I'm aware of - since then it's been driven Perth to Adelaide and back so I'd assume we'd have noticed if anything else wasn't working.

I'm pretty sure it started a week or so before I wired up a mirror-mounted reversing camera, front/rear viofo dashcam (hardwired) and number plate mounted led light bar, but now I'm doubting myself and wondering if I did something to cause the fan issue.

Any ideas?