Should be pretty straight fwd. I got 1 to do tomorrow.
The switch is located above the brake pedal, easiest to take off the lower trim near the drivers feet. You'll need a torx style driver to do that, or you may be able to get it with an allen key (bit rough though !). Have you sourced one yet ? I have found one for £4.04, think thats about the cheapest. Haven't had a price of Citroen yet !
I imagine its just a simply unplug and replug new one in :}
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Try fixfault.com to fix cars.